During construction process,there is a "principal-agent" relation between clients and constraints.Between the two parties,there exists moral risk under asymmetric information.This paper builds a "moral risk model" between clients and constraints during the construction process by applying "principal-agent theory" in the information economics theory.On the basis of quantitative analysis of the model,this paper draws some conclusions,which is benefitial to the enhancement of the level of project management.At last,this paper proposes some advice on reducing the moral hazard of the constraints.