Reliability of the product is established during the manufacturing process, process reliability can be reasonably and accurately measured by the stability of product performance and quality. For lack of research and assurance techniques of reliability formation in manufacturing process, grinding process stability is studied with the surface roughness seemed as focused quality characteristics. The grinding parameters and wearing-dressing condition of grinding wheel is the main factors affecting the grinding process stability. First, the qualitative theoretical research starts from the mechanism level, and on this basis, process stability is researched quantitatively. Method of Logistic regression can be used to establish the function between the grinding process parameters and product reliability during use. This method can also be used to distinguish the factors that influenced hardly, and guide the optimization of the manufacturing process to improve the reliability. Thereafter, distribution function of residual strength degradation with time-varying parameters is established by regarding product quality characteristics as strength and using requirements of quality characteristics as stress. After that, the model of reliability in use can be established with stress-strength interference model and it can be used to evaluate the reliability of products. Finally, by analyzing and optimizing the case, it can be proven that product reliability has improved significantly after optimizing.