In order to research the electromagnetic interference (EMI) in substation, this paper describes constitution of analysis model of EMI in substation secondary cable via which EMI can couple to substation secondary system. Substation cable is modeled by transmission line theory and calculated by finite difference time domain (FDTD) method. External electromagnetic field, lightning strike and busbar interference voltage are used to express EMI sources in their models. On this basis, simulation of every model is done and a few examples are calculated.