Abstract: Excellent chemical passivation can be achieved when the silicon oxide layer is applied to the silicon surface. However, high quality silicon oxide usually requires high process cost and time. This paper aims to improve the electrical performance of multicrystalline silicon solar cells by introducing ozone treatment and thermal annealing process without significantly increasing the cost. With the help of this treatment method, a thin silicon oxide layer with good quality is formed on the surface of silicon wafers, combined with the tandem silicon nitride deposited by PECVD can improve the final passivation quality of silicon wafers. At the same time, it is found that with the increase of annealing time, increment of minority carrier life is obviously strengthening, and the electrical properties of solar cell also increased. Finally, an absolute efficiency gains of over 0.5% was achieved by using this annealing process, and the optimal annealing process was found.