The jamming signal released by the enemy's aircraft can be explored by detecting the mutation of the received signal for radar seeker. The approximate entropy method, measuring the signal complexity, can be applied to process one frame data and to judge whether the jamming exists or not. Meanwhile, the moving-cut data approximate entropy is adopted to obtain the mutation point precisely. For three types of noise jamming and one deception jamming, the received signals of seeker radar are well analyzed respectively in intra-frame and inter-frame. The experimental results validate the effectiveness of the proposed algorithm in radar jamming detection, and for comparison, the wavelet transform is applied to detect the deception jamming, while the result validates that it is noneffective in noise condition.