Abstract: Common harmonic radar is hard to detect non-linear target under a complex background. To solve the problem, the detection technology of harmonic radar based on adaptive learning is researched. The paper introduces the basic principles of harmonic radar, designs the harmonic radar system in detail, and proposes the harmonic radar algorithm based on adaptive learning. Finally the harmonic radar is realized. The test and identification results show that the device can effectively realize the detection and identification of nonlinear targets under a complex background.