Taking system science as guidance,analyzing the existent pattern design methods in product development,this paper presented the conception of pattern system design.The pattern design methods having system characteristic was classified into two kinds:process pattern and object pattern.Based on the research of the two pattern design methods,their important effect and existent issues in product development were discussed.Through integrating process pattern and object pattern,a new pattern system design method was put forward,which was P-OI(Process-Object Integration) pattern system design method.First a group of design elements were abstracted which could reflect full objects and whole process,and then they were integrated into a system associated with each other according to some certain logical relation,so the pattern system integrated design object and design process was built.Besides the share and reuse advantages which common pattern system design possess,the pattern system design method also had the characteristics:system standard,process and object integration,system open,etc.The method provides a new kind thought for developing product design method in order to increase design efficiency,optimize design quality,and reduce development cost,especially predigest design of complex system.