Abstract: As product warranty design is largely limited to the unified warranty based on inherent reliability, it is proposed to associate field reliability with regional difference of the warranty period and develop a method for regional difference warranty period design based on field reliability. By analyzing the influencing factors of the warranty period, a polynomial fitting function is used to evaluate the product field reliability in different regions. And the prediction function for expected warranty cost and sales volume for each sub-region is developed. Furthermore, establish a novel high-dimensional optimization model that comprehensively considers field reliability, warranty cost, sales volume and price, and solve it with the evolutionary algorithm, so as to determine the optimal warranty period and price for different regions. Finally, the model is applied to optimize warranty design of air-conditioning. Compared with the traditional models, the proposed model can quantitatively evaluate the difference degree of warranty period in different regions, and has a significant partition warranty effect. Moreover, adopting a regional differential warranty period strategy is an effective way to reduce warranty costs and increase warranty benefits.