A dynamical model based on the photo-physics and photochemistry processes for superresolution photoinduced-inhibition nanolithography (SPIN) under both single-photon and two-photon excitation is developed and validated by experimental results. Numerical simulation results for the dot fabrication predict that the theoretical single dot size can be infinitely reduced, which shows diffraction-unlimited feature of the SPIN. A small reaction constant of the inhibitor polymerization is crucial to realize a small dot size and high resolution. It is discovered both theoretically and experimentally that the dot minimum size and best resolution occur under different inhibition beam powers because of the influence from the inhibitor polymerization. Moreover, due to the consumption of the photo-inhibitor molecules in the inhibition process, the dot size may vary during the sequential fabrication.