Abstract: In order to study the influence by pre-pulse discharge on capillary discharge pumped X-ray Laser, in this paper, a simplified XDCH code is used to simulate the process of pre-discharge with 2μs pulse width in polythene capillary filled with Ar. The plasma temperature, density and ionization degree calculated as initial condition are inputted into XDCH code to simulate typical main-discharge with 40kA. From the view of 1-dimension, some gain coefficient and electron density distributions with typical pre-pulse amplitudes are given. After analysis and comparison, conclusion is drawn that 100A pre-pulse with 2μs width can lead to higher gain. Two-peak structure in time spectrum and ring-like structure in space spectrum of 46.9nm laser line are predicted.