In order to evaluate wavefront of imaging systems, the wavefront gradient deviation evaluation methods were proposed, which could directly indicate imaging performance. The wavefront gradient deviation is defined as the deviation of image spot and image energy center, and the relative wavefront gradient deviation is the ratio of wavefront gradient deviation to Airy disk radius. The wavefront gradient deviation and relative gradient deviation can be evaluated by image size, image concentration and image energy distribution. Based on dozens of practical wavefront testing results, the evaluations of image concentration and image energy distribution are usually stable enough for different test resolutions. The difference of evaluation results is usually less than 10% for every double or half resolution. An aspherical wavefront and a spherical wavefront with dramatically ripple amount were analyzed to illustrate the relationship of wavefront gradient deviation and wavefront spacial distribution. Relied on the wavefront gradient deviation distribution on exit pupil and wavefront gradient distribution on image plane, it is convenient to operate for optical manufacture and assembling. The wavefront gradient deviation evaluations can be used as the wavefront specifications for quality control.