Abstract: In order to avoid the ionospheric folded clutter phenomenon,high-frequency ground radar signal requires a larger unambiguous range. Increasing pulse period is simple, but it will result in the decrease of the duty-cycle.However,HFSW radar needs high duty-cycle to ensure the detection range.To solve this problem, we use genetic algorithm to design double pulse orthogonal code, making the cross-correlation peak below respective autocorrelation side-lobe peak.The un-ambiguity distance of the signal is two pulse-cycles.Furthermore, we use inverse filtering to reduce the side-lobes of the new signal. Simulation experiments show it is better than the windowing weighted method,least squares method,recursive least squares method and owns better Doppler tolerance.