I found these two equations in MOS Capacitance Model section from Virtuoso Simulator Components and Device Models Reference.
In Triode region, the first equations works and the second one works for Saturation region.
Triode: Cgs= -(Cgg+Cgb+Cgd)
But in my Print DC table, I copied the values of Cgg, Cgb and Cgd. I find the Cgs always has a value very closer to the result got from Triode region equation verification even I am sure it is working in Saturation region.
Is there anybody who knows why?