The groove curved error in the grating can directly affect the diffraction wavefront quality of grating . Aiming at the problem, we established the mapping relationship between the grating curve error and the diffraction wavefront, built the optical path for measuring the curve error of the grating line, discussed the principle of the active control technology of the grating ruling machine, and used the active control technology to compensate the grating curve error on-line. Finally, we carried out the contrastive experiment to verify the feasibility of the method. The above method can compensate grating curved errors accurately and effectively, and the grating wavefront can be increased from 0.074 λ to 0.038 λ, increased by 48.6%, at the same time it can effectively solve the problem of the curve of the grating surface. The research results can be used to improve the quality of mechanical ruling grating, which has important theoretical and applied values.