A discussion based on software process improvement models such as ISO/IEC 15504,CMM,CMMI and Chinese software engineering criterion: SJ/T 11234?SJ/T 11235 etc is presented. There are comparisons among these models and their advantages and disadvantages are showed. The aim of this paper is to help the software organizations to get in touch with the latest international software assessment and improvement models and select a model that suit them best. So that their software abilities can be improved and they can produce software products with high quality, high efficiency and low cost.