what is the common mode voltage for ADA4700-1; and also please let us know any op-amp is having Vcm +/- 300V with single ended impedance of > 1M ohms
The input common-mode voltage range for the ADA4700 goes from V- + 3V to V+ - 3V. See below:
You can take a look at the AD8479. It can accept common-mode voltages to +/-600V, and has a fairly high input impedance.
May I ask what your application is?