Absorption boundary condition is an important condition for solving electromagnetic computing problem by Finite Difference Time Domain (FDTD) algorithm. First of all, four absorption boundary methods are selected, and the principles of Convolution Perfectly Matched Layer (CPML), Surface Impedance Boundary Conditions (SIBC) and the absorbers are derived respectively; FDTD algorithm is programmed and calculated by Matlab software. Then, the four methods are applied to two microstrip structures, the low-pass filter and the branch coupler, and the reflection coefficient is calculated. By changing the thickness of the air layer and the iteration step size, the four methods can get the correct results. Finally, the results of the two models are compared and analyzed in terms of computing time, memory usage and percentage of error. Compared to other absorption methods, SIBC has the least memory usage, higher computational efficiency, and an error percentage of 1.63%.