Coaxial rigid rotor helicopter using advancing blade concept (ABC) is capable of high speed forward flight. However large area of reverse flow region and intense blade tip compressibility brought by high forward speed put forward higher requirements for blade planform. In light of this, optimization design of coaxial rotor planform is conducted to impove forward performance by changing blade planform. Coaxial rotor flow-field is simulated by solving Reynolds-averaged Navier-Stokes (RANS) equations. An optimization method combining surrogated model and genetic algorithm (GA) is established based on aerodynamic simulations. The optimized blade features nonlinear chord distribution and tapered sweptback blade tip under geometry constraints when lift-drag-ratio is set as objective function. Compared with baseline rectangular blade, the optimized blade has a higher lift-drag-ratio (When the advance ratio is 0.6, the lift-to-drag ratio is increased about 30%), which proves the optimization is valid.