The present invention discloses a method for building an MOS transistor model enclosing statistical variation of noise, including: measuring noise in MOS transistors from different dies; creating a noise distribution diagram in accordance with the obtained noise data of the MOS transistors; adding a variation of noise parameter in at least one noise model file into a library file of MOS transistor to simulate noise in MOS transistors; if a simulation result does not cover the noise data in the noise distribution diagram, changing the variation of the noise parameter until the simulation result covers the noise data in the noise distribution diagram; if the simulation result covers the noise data in the noise distribution diagram, adding corresponding variation of the noise parameter into the library file of MOS transistor as the MOS transistor model enclosing statistical variation of noise. The model obtained by the present invention is more precise.