The non-isothermal crystallization process of poly(ethylene terephthalate) at different nucleation mode were researched by using Monte Carlo simulation. The results showed that the value of Avrami exponent near to the theory value 3 at predetermined nucleation mode when the experiment data were deal with the Ozawa equation. Under the condition of the sporadic nucleation, the values of Avrami exponent were intervenient 3 and 4 with the number of nucleic linearity increase to some value. It was showed that when the number of nucleic attains to some value the nucleation mode was change from sporadic nucleation to predetermined nucleation.