An imaging apparatus of monocular multi-view was designed by putting a symmetric bucket cavity, which was made by 4 planar mirrors, in front of the camera. An image of the pear surface from different perspectives could be obtained by this device; then, a variety of views which present pearl quality could be obtained by image processing. Finally the quality of the pearl could be determined by feature fusion. Experimental results show that the image captured of pearl entire surface could be obtained in a unified color system by the proposed device. Besides, the device accomplishes pearl online detecting and grading according to the quality indicator such as size, shape, luster, blemish and color.