zhè shì yí gè mìmì.

A simple breakdown is:

• 这 = this
• 是 = is / to be
• 一 = one, and here it helps express a
• 个 = a classifier or measure word
• 秘密 = secret

So the structure is:

• 这
  • 是
    • 一个秘密
• this
  • is
    • a secret

This is a very straightforward A is B sentence.

This is because of a common tone change rule for 一.

By itself, 一 is normally yī with first tone. But in normal speech:

• before a 4th-tone syllable, 一 changes to 2nd tone → yí
• before a 1st-, 2nd-, or 3rd-tone syllable, it usually changes to 4th tone → yì

Here, the next word is 个 gè, which is 4th tone, so:

• 一个 is pronounced yí gè

So the written character stays 一, but the pronunciation changes.

Because Chinese usually needs a classifier between a number and a noun.

In English, we say:

• a secret
• one secret

In Chinese, that pattern is usually:

• number + classifier + noun

So:

• 一 + 个 + 秘密

The word 个 is the classifier here. English does not have this kind of word in most cases, so it often feels strange at first to English speakers.

Yes. 个 is the normal, natural classifier here.

个 is the most common general classifier in Mandarin, and it is often used with many nouns, including abstract things in everyday speech. So 一个秘密 is completely normal.

You will learn more specific classifiers for some nouns later, but in this sentence, 个 is exactly what you want.

Yes. 这是个秘密 is very common and natural in spoken Mandarin.

Both are correct:

• 这是一个秘密
• 这是个秘密

The version without 一 sounds a little more conversational and compact. This kind of shortening is very common in speech.

Usually, no—not in normal everyday Mandarin for this meaning.

To say This is a secret, Chinese normally wants:

• 这是一个秘密
• or 这是个秘密

Without 一 个, 这是秘密 sounds unnatural in most ordinary situations.

So for learners, the safest choice is:

• 这是一个秘密
• or 这是个秘密

Not exactly.

In this sentence, 是 works a lot like English is because it links one noun phrase to another:

• 这 → 一个秘密
• this → a secret

But Chinese does not use 是 in every place where English uses to be.

For example:

• 他很高 = He is tall
  not 他是高

• 他在家 = He is at home
  not 他是家

So 是 is mainly used when one thing is being identified as another thing, especially with nouns or noun phrases.

Yes, in this sentence it is very close to English.

The pattern is:

• 这 = this
• 是 = is
• 一个秘密 = a secret

So the order matches English nicely:

• This is a secret.

That said, this does not mean all Chinese sentences follow English word order. It just happens that this one is very similar.

The zh sound is a retroflex consonant in Mandarin.

A simple learner-friendly way to think of it:

• start with something like the English j sound
• but curl the tongue slightly farther back

So zhè is not exactly like English jay or juh, but that rough comparison can help at first.

Also:

• zhè is 4th tone, so it falls sharply
• it should sound short and firm

Try saying it as one quick falling syllable:

• zhè

A natural pronunciation is:

• Zhè shì yí gè mìmì.

A few pronunciation notes:

• 这 zhè = 4th tone
• 是 shì = 4th tone
• 一 yí = 2nd tone here because of tone change
• 个 gè = 4th tone
• 秘 mì = 4th tone
• 密 mì = 4th tone

So the tones are:

• 4th, 4th, 2nd, 4th, 4th, 4th

When several 4th tones come together, native speech often sounds a little smoother than a beginner’s very separate, heavy pronunciation. But as a learner, it is fine to pronounce each tone clearly first.

In normal Chinese writing, words are usually written without spaces.

So this sentence is normally written as:

• 这是一个秘密。

Teaching materials often insert spaces to help learners see the parts more clearly:

• 这 是 一 个 秘密

So the spaced version is for learning, but the normal written form has no spaces.

It is the Chinese full stop, the equivalent of the English period .

So:

• 这是一个秘密。

means the same kind of sentence ending as:

• This is a secret.

Chinese punctuation uses some marks that look different from English ones, and 。 is one of the most common.