Abstract: Variable pitch thread is widely used in plastics, rubber and food industries. Variable pitch thread, especially equal tooth width variable pitch thread, is a difficult point in NC machining. The main difficulty lies in programming. So far as I know that automatic programming software at home and abroad can not program this kind of thread precisely. They have to use manual programming. This element is used in the numerical control lathe project of the first national skills competition held not long ago. This is a beneficial attempt to combine the competition with the actual production. The author makes a detailed analysis of the variable pitch thread with equal tooth width in exam problems, introduces a variety of solutions from right to left and from left to right, and provides a set of verified programs for each. The program from right to left has the advantages of easy to understand, easy to program and convenient to repair tooth width.