Free-space optical communication has many advantages over traditional communication. Improving the coupling efficiency of free-space optical communication (FSOC) receivers is of great significance for the quality of communication. We used tapered fibers in optical coupling. Based on the simulation results using the BPM algorithm, tapered fibers with low loss transmission were prepared using a fusion taper method. First, the mode field transmission characteristics of the tapered fibers and double tapered fibers were studied. Second, the difference in coupling efficiency and transmission efficiency between multi/single mode fused fibers and tapered fibers was studied using a static spatial light-fiber coupling experiment. The lateral offset tolerances of the coupling efficiency of these two fiber structures were also studied. The results show that the tapered fibers have good filtering characteristics for matching single-mode optoelectronic devices in the back end. They also have higher lateral offset tolerance characteristics than common fibers and a high transmission efficiency of around 70% that demonstrates low-loss transmission characteristics. Therefore, tapered fibers can be widely applied in the optical coupling of FSOC receivers and mode converters.