A method of detection of rice kernel shape based on region span searching is proposed,in which the length and width of region circumscrihing rectangle are used as the region spans,and the method of searching of the length and width of rice kernel by rotating of the circumscribing rectangel of rice kernel is firstly proposed in the paper,the rice kernel shape is derived from the searched length and width. Due to the simultaneous rotary searching of the spans in two orthogonal directions in rice kernel region,the length and width of rice kernel are completdy found out under rotating of the circumscrhing rectangle up to 90 degree. Our experimental results showed that the proposed method is characteristic of the invariance for rotation of rice kernel,and the result of detection of rice kernel shape using the proposed method is eoinddent with that of manual inspection with the relative error of 1.73%.