In industrial production, neglected loading of metal parts is very normal. It not only causes the quality reduction of products, but also affects production rate. Based on the theory of electromagnetic induction, by supervising the assemblage process of metal parts, it is able to count the number of assembled metal parts so that automatic online monitoring of neglected loading can be achieved. The feasibility of using the eddy current method to monitor the motions of metal parts is analyzed theoretically and MATLAB is utilized to simulate. On the basis of theoretical analysis, the specific eddy current type transducer, the appropriate signal-processing circuits and the software are designed. A testing system is established for analog. This method can effectively solve the problem of neglected loading by artificial factors, save the costs of factories, raise the FPY of products.