Since 2013，Public-Private Partnership（PPP）has played an important role in China’s infrastructure investment. At the beginning of the implementation of PPP mode，investors calculated the project internal return（IRR）by assumptions from bidding documents，As the project progresses，those assumptions have changed due to dynamic project advancement，which leads to the real IRR different from the initial IRR. Especially investors have to adopt dynamic investment management decisions to control adverse changes in project execution，such as delay of loan，downsizing of profitable investments contracts，rising of operating costs. This paper provides a new dynamic investment decision management method to help PPP projects investors timely grasp the impact of project assumption changes on IRR and explain how they are used in decision-making process.