Abstract: In order to simulate the electromagnetic fields with complex structure in two dimensional, the Finite IntegrationTime Domain (FITD) method based on triangular cells was studied. Finite Difference Time Domain (FDTD) method and FITDwere applied to compute the cut-off frequency corresponding to the mode of ideal circular waveguide with the radius of 0.085m.The results show that the relative error between results computed by FITD method and the theoretical value is smaller than thatbetween results computed by FDTD method and the theoretical value, which proved the superiority of the FITD method.