how to export TSMC90NM cadence pdk to ADS

If there is a ADS Design Kit of your process, install it as usual.

but the foundry just give me the cadence version ,how to extract the netlist or something like that to the ADS?

You can't do that.

Can i extract the spice model?

edit:

Yes, in ADS you can include SPICE netlist. What are you trying to do?

I have try it ,but failed,do you have any tutorial? Or tell me the steps....

Any ideas?

The process models are probably crypted in PDK that's why you can not extract it into SPICE format.The foundries generally do so...

can i simulate the S-PARAMTER of mos and put it to ADS,S-PARAMETER is small-signal model,i use this method to simulate vco ,is it OK?

VCO's are not simulated with s-parameters, you should use nonlinear model of your component.
You may perhaps find loop gain and loop phase to find out the oscillation frequency of your VCO only and it won't be a good reference for you.Because s-parameters are small signal parameters and they don't never reflect the nonlinear response of your active device.