In the process of purifying polysilicon by metallurgical method,the temperature control function and curve of annealing theory are explored by mathematical modeling of different annealing temperature schemes. The mathematical model shows that the silicon ingot is directly insulated, depending on the natural thermal equilibrium annealing, the internal stress is greater than the critical stress of generating dislocation. The top heater is used to heat the top of the silicon ingot to reduce the cooling rate. By comparison, a lower annealing temperature of 1236℃ and a shorter annealing time 8.52 ks is chosen as a reasonable theoretical annealing control scheme.The experimental results show that the annealing scheme has the advantages of less visual crack and a few carrier lifetime and resistivity.