The continuous operation mode of high equilibrium in the flow construction yields great benefits in lowering the cost and reducing the construction period as well as risks. The change of the construction period of any sub-construction will definitely exert a relatively great impact on the balanced construction of the project. Through the analysis of Monte Carlo simulation method (MC), the assurance degree of the total duration calculated by using the traditional method is extremely low; after considering the effect of several kinds of important risks during the flow construction, such as “Adverse Selection”, “Student Syndrome” on the total construction duration, the assurance degree of the total duration goes to almost zero degrees. The measures for the corresponding risks are put forward and their effects are analyzed as well. After the corresponding measures are adopted, the assurance degree of the total duration of the project has been greatly increased.