Operational principle and output characteristics of fiber laser were studied based on the rate equation.The threshold term and expression of output power of fiber laser were given at steady state. Using numerical simulation results,basic parameter of fiber laser was analyzed and demonstrated, and which is the theoretical basis for optimized design of fiber laser.Experimental method of all fiber structure fiber laser was put forward.Single-mode continuous laser output was realized,which is maximal power of 7.5W,wavelength of 1080 nm and half maximum full width of 0.11 nm.