With castor oil-based lube as an object investigated,degradation test for the synthetic lube was implemented under not a single degradation factor.Based on the biodegradation of the given lube,one new abiotic degradation factor,photodegradation was supplied to simulate the true degradation process of the given lube in the natural environment and further to establish the lube’s degradation testing method in lab under not a single degradation factor.Infrared spectrometry was used to measure the remained content of the lube after degradation,and the lube’s degradation rate was counted.The results show that the testing data from the new testing method possess excellent stability and repeatability,and show relatively good consistency with the results reported in the references.The photodegradation rate of the lube is also acquired from the new testing method.Although the value is relatively low,the influence of light on lube degradation can not be ignored.