given certaion resource, what the index/search performnce when shard number are changed?
I am not aware of any article. If there were any, they would be about some specific usecase though. Reality is that there is no single/definitive answer to this question. It depends on a lot of factors: how many documents you have, their size, what features you use (query, aggs, suggestions, highlighting...).
I think the correct answer is test, test, test...with your own real data and queries. That will give you much better answers than any article you can find 
I don't agree with u complete.
Although index perfromance is heavily related to document, still u guys give us a benchmark.
the same thing, all I need is a Qualitative conclusions， not Quantitative conclusions
What benchmark are you referring to?
Well in general "more shards may mean more index performance/ search performance", but you got to have enough nodes to allocates the shards into. And you need to find a good compromise cause if you go with too many the cost of sharding is more than the gain. These generic answers can be interpreted in some many ways. Really, if you want a good answer that works for you, test it with your data
the benchmark:
https://benchmarks.elastic.co/index.html