This paper presents a performance optimization of solar multi-stage flash (MSF) desalination process using Pinch technology. Three different situations were studied by using pinch analysis in this paper, respectively. Firstly, the distilled water is not discharged in each middle stage. Secondly, the distilled water is discharged in each stage. Thirdly, the distilled water is discharged every 5 stages. Pinch charts at different situations are given. At the same stage temperature difference (2 k) and pinch point temperature difference (2 k), the first situation has a higher gain output rate (GOR), about 17.5, and the second and third have lower GOR, around 9. However, GOR is easily influenced by abnormal stage temperature difference at the first situation, and but not in the second and third. The GOR rests on the working temperature range of MSF and the sum of both the maximum stage temperature difference and pinch point temperature difference. To enhance the GOR, it is suggested that we should use the wide working temperature range of MSF, not pumped out the distilled water at middle stages, and keep the same stage temperature difference without fluctuate.