Abstract: In automatic reading system of index-instrument,image of dial plate needed be read must match template in order to decide type and range of instrument needed be read.However,traditional template matching algorithm has bad antiinterference ability for geometric distortion dilation,rotation of image. Circle partitioning matching method has certain anti-interference ability,but low matching accuracy.The paper proposed loop matching method on the basis of circle partitioning matching method,which used picture element of loop to calculate sum and calculate characteristic value to realize matching.The experiment result showed that the loop matching method has good anti-interference ability,better matching accuracy and good practical application value.