The jib is an important component for the tower crane. The reliability of the tower crane jib has a direct impact on the safety production. In the current crane industry, the traditional allowable stress method is still the main method for designing tower crane jib. As a result, the reliability of the tower crane jib cannot be given quantitatively. In this paper, by using the probabilistic method, the reliability of a tower crane jib is worked out, and a design way based on the reliability for the tower crane jib is provided.