The opposite of "cha hen duo" is "chabuduo"
You might be used to thinking of 差不多 (chàbùduō) as a single word, and that's totally OK. But if you want to negate the whole idea of rough equivalency, then you need to think of it as a phrase and use 差很多 (chà hěn duō). Not surprisingly, it's a little less versatile than 差不多 (chàbùduō).
When 差不多 (chàbùduō) is a predicate, it literally means "the difference is not much." The opposite, then, would be 差很多 (chà hěn duō), which literally means "the difference is very great." Less literally, if 差不多 (chàbùduō) means "more or less the same," then 差很多 (chà hěn duō) means "not the same at all" or "very different."
Subj. + 差很多
A + 跟 / 和 + B + 差很多
- 中西方 的 文化 差 很 多 。Chinese culture and western culture are quite different.
- 这 两 个 词 的 意思 差不多，但是 用法 差 很 多 。The meanings of these two words are basically the same, but their usages are very different.
- 她 和 她 老公 的 年龄 差 很 多 。There is a big difference between her age and her husband's age.
- 公司 今年 的 收入 跟 去年 差 很 多 。The company's income of this year is a lot less than last year.
- 这个 服务员 和 经理 的 服务 态度 差 很 多 。There is a big difference in the attitude between this waiter and his manager.
- 我 的 生活 习惯 跟 我 父母 差 很 多 。My life habits are very different from my parents'.
- 两个 老师 都 很 好 ，不过 他们 的 学历 差 很 多 。They are both great teachers, but their education are very different.
- 老 版本 跟 新版本 的 功能 差 很 多 。There are huge differences in the features between the old version and the new one.
- 这 两 件 衣服 看起来 差不多 ，但是 质量 差 很 多 。These two pieces of clothing look pretty much the same, but their quality is very different.
- 他们 是 双胞胎 ，但是 两 个 人 的 性格 差 很 多 。They are twins, but there is a big difference in personality between them.
- Approximations with "chabuduo"
- Expressing "almost" using "chadian mei"
- Expressing "almost" using "chadian"
Sources and further reading
- 现代汉语八百词（增订本） (pp. 111) [ →buy]
- Integrated Chinese: Level 2, Part 1 (pp. 54-5) →buy
- Basic Patterns of Chinese Grammar (pp. 116) →buy