As a bridge assessment method, risk assessment is more and more applied to load-carrying capacity assessment of existing bridge. This method assesses the bridge through the failure risk value which calculated by the failure probability and failure loss value. The most important factor to the risk assessment of load-carrying capacity upon the existing and diseased bridge is the calculation of failure probability. This paper combines the reliability calculation theory with a certain site detective data of bridge that considering uncertainty of load and resistance along with the diseases of bridge, and induces in the correction coefficient of load and resistance respectively to calculate the failure probability and reliability index of bridge. Finally, these indexes are compared with those provided by the current code to implement risk assessment of load-carrying capacity of the bridge.