With aim to enhance the output intensity of X-ray laser(XRL)under the condition of low pump energy,theoretical analysis and numerical simulation were presented on double prepulses and also curved target techniques. The simulation results indicate there is a good pulse structure of 2 ns/5 ns(2nd prepulse dalay/main pulse delay)that can optimize the gain area of plasma. The XRL experiment of Ne like Cr(J=0-1,3p-3s transition)pumped by the double prepulse was performed on “XingGuang Ⅱ” laser,and a 28.5 nm single line XRL was achieved,as well as other significant results. The XRL output intensity shows much reliance on the last prepulse energy when the delay time is fixed. The experimental and calculation results show good consistency.