Initial trust plays a key role in engineering construction and is the basis of the relationship between owners and contractors. In order to analyze the motivational mechanism of initial trust between owners and contractors, the authors construct the mechanism model of the initial trust between the owners and the contractors with the factors of trust propensity, faith of the trust, the characteristics of the trustee, the institutional trust and the trust motivation, and conduct the questionnaire survey and empirical analysis of structural equation model from the view of the owners. The result shows that the institutional trust, characteristics of the trustee and trustful faith of the trustor have a clearly positive effect on the trust motivation, and the characteristics of the trustee has a significant effect on motivation of the trustor, while the trust propensity of trustor has little influence on motivation of the trust. The result reveals the important insights on the building of initial trust of the owners towards contractors.