Contract flexibility and its analysis has been used in the construction project contract management widely. However, the existing research results have not agreed on the connotation and dimension of contract flexibility, which leads to insufficient empirical studies on project performance due to contract flexibility in construction project. Based on the whole process risk sharing perspective, this study determines the scale of contract flexibility with quantitative methods. Research shows that the contract flexibility can be divided into 3 dimensions: Price Flexibility, Control-right Flexibility and Renegotiation Flexibility. Among them, Price Flexibility is the contract terms corresponding to the initial risk sharing; Control-right Flexibility can transfer the control-right according to the environment corresponding to the risk re-sharing process; Renegotiation Flexibility is the re-contract to deal with the risk re-sharing in the contracting process. The results provide a complete analytical framework for the contract flexibility, and lay a theoretical foundation for the empirical research of the contract flexibility on the contractor's performance behavior.