The paper focuses on quality improvement strategy for manufacturing process. When the manufacturing process is in abnormal condition, managers applied all kinds of quality-improving strategies to keep their product qualities stable. Besides, different quality-improving strategies have very complex relationship between quality costs and revenue. In this paper, we proposed an incremental profit model to find out the best quality-improving strategy. Considering the products could be repaired, we assumed that the characteristics of products is normally distributed with known mean and variance, and assuming a reasonable improving cost and expect profit structure to obtain the optimal process mean and variance. Furthermore, we also develop a numerical example to illustrate the meaning of this research and the result, which could be used by the later researches and actual applications.