The basic principles of algorithm based on the LOG operator’s local dynamic threshold and the maximum between clusters variance’s global thresholds are respectively analyzed. The specific algorithm of binarization is detailedly discussed in digital recognition of mechanical workpiece. For their advantages of dynamic threshold and global threshold and in view of the characteristics of workpiece character, a new method is proposed and combines the local dynamic threshold grounded on the LOG operator with the global threshold of maximum between clusters variance. To begin with, the confusing and resemblant figures characters can be easily distinguished by using local dynamic threshold algorithm of LOG operator to enhance the details of characters. And then the binarization of image background is executed by use of the global threshold algorithm of maximum between class clusters. The integrated algorithm has good performance in many aspects such as computational complexity, implementation time, binarization effects and the scope of application. It has been applied to the actual system and achieves good results.