A four-wave mixing (FWM) model is used to analyze the polarization control of terahertz (THz) pulse generated by a two-color laser field in air. The analytic formula for the THz intensity varying with the THz polarizer angle, and the relative phase between the two pulses, are obtained. The corresponding numerical results agree well with both numerical result obtained from a quantum model and measured data reported. Moreover, possible phenomena are predicted for variables not found in other experiments. Compared with the quantum model, the FWM model gives analytic formulas and clear physical pictures, and has the advantage of efficient computing time.