There are important applications of metal in metamaterials. Three methods for dealing with metal in FDTD are analyzed and compared. ADE(auxiliary differential equation method) and PLRC(piecewise linear recursive convolution) have the same numerical result. However, there is a little difference between Sakoda's method and ADE. It is due to the error in calculation of convolution integral with Sakoda's method. Improving the convolution integral with the method used in PLRC, these three methods give the same results.