In allusion to the fact that it is hard to judge the shadow of photovoltaic (PV) module, a shadow judgment method based on peak counting and parameter identification is proposed. Firstly, the I-V output characteristic curve of PV module is scanned globally and quickly through programmable DC electronic load, which is used to record the number of noticeable peaks. Then, an improved artificial fish swarm (IAFSA) is adopted to identify the internal equivalent parameters of PV module by sample values of I-V curve, and combining with the root mean square error (RMSE) to determine the slight shadow of PV module. The shadow condition of PV module can be effectively judged through the two-step method, the experimental results further demonstrate the effectiveness and accuracy of this method. This work is supported by Innovation Project of Postgraduate Education of Jiangsu Province (No. CXZZ12_0228).