A resonant power converter and a frequency tracking method for a resonant power converter are disclosed to determine a resonant status of the resonant power converter by sampling a secondary current, thereby controlling frequency of a drive signal. Therefore, the frequency of the drive signal tracks resonant frequency of the resonant power converter. The resonant power converter includes an inverter branch, which connected to the inverter branch, a transformer connected to the resonant branch, and a rectification and filtering branch connected to the transformer. A primary side of the transformer is connected to the resonant branch, and a secondary side of the transformer is connected to the rectification and filtering branch. A detection branch is connected to both the secondary side of the transformer and the rectification and filtering branch.