The phase-comparison method in frequency domain is usually used in the angle measurement by the conventional CW radar. Based on amplitude-comparison method in frequency domain, a new algorithm of low-angle measurement by CW radar is proposed. An investigation is made to expose the relationship between phase-comparison method and amplitude-comparison method, with the conclusion that the amplitude-comparison method in frequency domain can be used in the angle measurement by the CW radar. Furthermore, the utility of the C²algorithm is also studied, Additionally, a new algorithm of low-angle measurement of CW radar is given. Experimental results show that the proposed algorithm is effective for tracking the target in low-altitude environment.