The coupling efficiency of the backscattering optical field received by the telescope into single-mode fiber is one of the significant parameters affecting all-fiber Raman lidar system. By analyzing the mathematical model of coupling the free space plane optical field into single-mode fiber, the influence of the telescope central obstacle in the coaxial lidar on the optimum coupling efficiency is clarified. And then it is numerically analyzed the change of the coupling efficiency with the variation of the alignment errors such as the lateral offset, tilt angle and defocus error with different obstacle ratios. Furthermore, based on these conclusions, an initial optical system is constructed for the telescope coupling system optimization. By adding and choosing suitable lenses and micro lenses and optimizing the configuration parameters, the total coupling efficiency of 17% with the Cassegrain telescope is enhanced to 50% when the obstacle ratio is 0.288. Two coupling configurations with micro lens arrays and fiber arrays are designed to improve the coupling energy of light signal. Simulation results show that the coupling efficiency and energy may be improved using the new telescope coupling system with micro lens array and single-mode fiber array.