For the fatigue failure of the excavator working mechanism, a kind of prediction method to fatigue life based on the measured load history is proposed , which will give an important reference for the safe-checking and repair of the working mechanism during its employment. By using the strain measurement system, the load histories of the weak parts are measured in the paper. The load his tories are analyzed with rain-flow counting method, and the structural S-N curve is corrected based on the fatigue test data of the material. The fatigue life of every test point is estimated by using the nominal stress method, which achieves the goal of fatigue life prediction of the working mechanism. This method can also give reference for the similar mechanism.