hi, can i load coming data compressed on json and decompress it on android?
Is you data compressed like zip, rar… or just in json format?
In any case you can use open source .NET libraries for zip to uncompress just search for .net zip library you will find bunch of them.
For json you have JsonUtility now as part of Unity API or if you wish also many open source libraries for handling json are also available.
I hope this answers your question.
my data is coming json but i heard that i can load that data compressed and then unzip on my device, and that saves downloading? correct if iam wrong 
Just to be clear you have to first compress json data then send it to your device:)
Really roughly I would say if you need some huge chunk of data downloaded like first time you run game some additional content etc. then it has sense you would save on download size.
Otherwise you need to weigh the issue because decompressing also takes time on device so depending on your architecture perhaps you need to rethink it if you need to archive json files it all depends on what your game does and how did you envision it.
For decompressing, this zlib works fine,
http://answers.unity3d.com/answers/176022/view.html