The optical matrix under paraxial approximation can make the calculation of optical transmission easy and convenient in designing optical system. The ABCD transformation matrix method for the coupling optical system design is introduced, using the ABCD law of the Gaussian beam. The design of a coupling system of semiconductor laser diode to single-mode fiber is given in detail; additionally, the changes of the coupling loss with the coupling distance of the system are calculated, and then the recently reported results are compared, they roughly agree with each other, which shows the method is feasible. From the whole design and the calculation for coupling efficiency, the ABCD matrix makes the design easier and reduces the cumbersome calculation. Compared with general diffraction calculation, it is a convenient and effective method and it can give some instructional suggestion for fabricating the semiconductor laser diode coupler.