In China，more and more PPP projects have been entering into construction and operation periods，and many of them have facing problems such as investment overruns and exceeding budget estimates. If these problems are not dealt with in timely and appropriate manners，they will affect the smooth implementation of the projects，and in some cases even generate more serious conflicts and disputes. However，the adjustment of investment budget estimates is another key and difficult point in the management of government investment projects. This paper analyzes the main reasons for exceeding budget estimates of PPP projects，and sorts out the main legal and policy basis for adjusting the budget estimates of PPP projects. Then，the paper proposes that the key to good works on PPP projects budget adjustment should deal with three aspects of the relationship between budget adjustment policies and regulations and PPP contracts，further it analyzes and proposes specific implementation principles and steps for budget adjustment，and finally it puts forward relevant measures and suggestions from five aspects，such as deepening the pre-project work and strengthening design.