Abstract: Based on the industrial testing specifications and the rectangular characteristic of the test sieve, this paper proposes an automatic measurement algorithm on intersection angel of longitude line and latitude line by combining with the modern image processing measures. The proposed algorithm adopts the improved Harris method to avoid the missing and false detection and the dependence on threshold value setting of the traditional Harris. Moreover, the sub pixel edge detection is combined with both Canny algorithm and the polynomial fitting to achieve the extraction and fitting of the angle edge. The experimental results show that the proposed algorithm can attain the requirement of industrial measurement within the error range.