Abstract: To analyze the influence of the side cascaded coupler on the fiber laser, the parameter of self-developed (1+1)×1 cascaded couplers and commercial combiner of(2+1)×1 was discussed. In the experiment, the coupling efficiency, translation loss of pump power, and the insertion loss of signal power were measured about the two couplers, and based on the two types of couplers, the study of all fiber lasers was carried out. In the fiber laser with the (1+1)×1 coupler, 344 W of 1 080 nm was obtained with the 975 nm pump power of 433.8 W, and the optical to optical conversion efficiency was 77%. In the fiber laser with the (2+1)×1 coupler, when the pump power of 975 nm was 433.8 W, the output power of 1 080 nm was 260 W with the optical to optical efficiency of 60%. Comparison of two types of fiber lasers show that for the (2+1)×1 coupler, it is difficult to realize the cascaded structure due to the large transmission loss. However, the (1+1)×1 side coupler can achieve 5 cascaded structure with small transmission loss.