We propose a surface plasmon (SP) structure in electrically pumped multiple graphene-layer (MGL), and calculate the functions of dynamic conductivity and absorption coefficient. Meanwhile, the dependences of absorption coefficient on different factors are simulated. SP can get gain when absorption coefficient is negative, and the SP gain can be enhanced by lowering temperature, applying high bias voltage and choosing the graphene with proper layer number and long momentum relaxation time. The study on SP gain is hopeful to be used in amplifiers and graphene-based plasmon devices.