What is the maximum value for a drop down list?

You mean the number of choices? I do not know of a concrete limit. But performance and UX will degrade when that number becomes 3 digit or more.

Yes, mean the number of choices, And after how much number of choices performance will impact 

There's no one-size-fits-all answer for the exact number where performance dips in dropdowns.
Large datasets in dropdowns can slow things down. I would suggest, For a faster search, Users simply type 3 or more characters to narrow the list and find what they need quickly. This keeps things speedy and user-friendly.

I agree with Stefan that if you have more than about 100, you should consider using other options, such as cascading dropdowns or pickers. The only exception to that is if you have something where there are a large number of familiar values - for instance, I'd rather have a dropdown for all countries, even though there are ~200 of them.

It's hard to answer what the performance impact will be except to say, the more options you have the slower it will get. It is highly dependent on what your data source is, how you're querying / manipulating the data, etc.