How to simulate the IIP3, NF of a non-50 ohms input circuit?

For a circuit whose input impedance is high, how to simulate its IIP3, gain, NF so that I can use these parameters to calculate the IIP3, gain, NF of the overall cascade chain?

If the input impedance is high, and the source impedance is low, it is merely a buffer amplifier. It is not optimized for maximum power matching at the input but in case of a buffer amplifier that's not what it is used for, it simply cannot load the source.

About the noise figure: instead of looking at NF, you can look at the voltage noise at the input. This contribution will be dominant above the current noise.

For the gain you can resort to voltage gain. That what you're interested in: Does the buffer change the size of the magnitude?

Finally the IIP3 again can be referred to as an input voltage. Think of your amplifier as a system with an input and an output. It doesn't matter what type of I/O that is, it can be voltage, current, power, anything.

Thank you for you explaination.
A more question is that I want to calculate the overall NF, IIP3, gain with the formula F=F1+(F2-1)/G1+...., IIP3=......
Does these formulas stiil valid when I use your methods to determine the NF. IIp3 of each stage?