This paper describes principles and applications of an adaptive order tracking diagnosis technique for fault diagnosis in rotating machinery. An adaptive high-resolution order tracking method with a variable step-size affine-projection algorithm (VSS APA) is used to diagnose faults in the gear-set and centrifugal fan blades. In comparison with conventional order-tracking methods such as recursive least-square filtering algorithm, the proposed VSS APA technique has fast convergence speed for adaptive filtering process. The VSS APA-based order-tracking technique can overcome problems encountered in FFT based methods. The smearing problem is treated as the tracking of frequency-varying band-pass signals. Ordered amplitudes can be calculated with high-resolution adaptive filter algorithm after experimental implementations carried out to evaluate the proposed algorithm in gear-set and centrifugal fan blades defect diagnosis. The experimental result indicates that the proposed algorithm is effective in rotating machinery fault diagnosis.