This paper converts a time domain non-stationary signal to an angle domain stationary signal using a computed order tracking(COT) method, which combines the advantages of both the traditional order analysis algorithm and kurtogram algorithm. The transient impact force of the fault vibration signal from the rolling bearing was valued by the kurtosis index, and the COT-kurtogram algorithm was thus proposed. Both the simulation and practical results demonstrate that the COT-kurtogram method can effectively identify the envelope demodulation bandwidth parameter in the order-domain, and significantly improve the accuracy of the fault feature extraction of rolling bearing in varying speed working conditions.