I want to design a low-past filter key but I dont know which op amp I need to use? I want to op amp's open loop gain is higher. Can anyone help me?

 

Open-loop gain is pretty high for most all op-amps nowadays so any should do.

What is the bandwidth you are wanting to operate the filter with? What is the supply range that you want to power the op-amp with?

Btw it's low pass not low past.

 

Like blah said, first step is to determine the frequency that you want to pass and frequency that you want to filter out.

Since you don't know what those frequencies are, there is no point to continue.