A selfdeveloped precipitation microphysical characteristics sensor was applied in field experiment and a large quantity of raindrop images were obtained. The causing reasons and handling methods for outlet raindrop images were discussed, and a vectorized method based on the Akima interpolation under the polar coordinate was proposed in this paper. Then, the characteristics of average raindrop shape and axis ratio distribution were analyzed. The results show that the small drops (<1 mm in diameter) have spheroids shapes, the moderate drops (<1.0 mm and <3.0 mm in diameter) have oblate spheroids shapes and the larger drops (>3.0 mm in diameter) have more bulged tops and flattened bases. The mean axis ratio distribution is in good agreement with the empirical relationships, and the deviation between them is smaller than 0.04. The raindrops ranging from 3.4 to 3.8 mm are more spherical than those from empirical model.