Using the energy transmitting fiber to replace the optical guide arm can greatly improve the flexibility of the medical handle, reduce the complexity of the system and improve the efficiency of laser transmission. A 2.79 μm Er, Cr: YSGG laser and its fiber coupling system were designed and developed. The influence of the output mirror of the laser resonator on the parameters of the output Gaussian beam was analyzed. A meniscus type lens was designed as the output mirror of the laser resonator to reduce the divergence angle of the laser beam, and a suitable coupling single lens was selected to meet the coupling conditions of the ZBLAN glass fiber with a numerical aperture of 0.29 and a core diameter of 400 μm. The experimental results show that when the meniscus type lens is used as the laser output mirror and the focal length of the coupling lens is 20 mm, the coupling efficiency of the laser transmission can reach up to 83%, and the maximum transmission power is 6 W, which meets the clinical application requirements of the laser medical instrument.