针对目前脉冲硬X射线源能谱硬、辐照面积小、辐射场电子份额高无法开展系统电磁脉冲效应实验研究的技术难题，提出了采用复合薄靶软化脉冲硬X射线能谱、降低电子份额的方法。采用MCNP程序数值模拟了电子和光子在不同材料中的输运规律，分析了复合靶结构和材料厚度对X射线能谱、电子份额的影响。以“闪光二号”加速器为电子束源，设计了复合薄靶、X射线窗。实验得到的X射线参数：平均能量121 keV;均匀性2∶1情况下，700 cm2平均剂量40 rad(Si)，500 cm2平均剂量170 rad(Si);光子数与电子数的比值大于103，可以开展系统电磁脉冲效应初步实验研究。

Bremsstrahlung source with high energy electrons will produce a substantial excess of high energy photons, and these photons and electrons severely degrade the fidelity of system generated electromagnetic pulse(SGEMP) simulations. Thus, the development of composite thin converter were undertaken to achieve a high fidelity of X-ray source, using high Z material with small thickness to lower photon energy and low Z material to filter the transmission electrons. The influence of converter thickness on X-ray parameters was analyzed by using MCNP code. And a composite converter was designed for flash-Ⅱ accelerator based on the simulation result. Experimental result shows that the average energy of photons is 121 keV, the dose on 700 cm2 area is more than 40 rad(Si) and it is 170 rad(Si) on 500 cm2 area. The uniformity is less than 2∶1, and the ratio of photons to electrons is more than 103. The proportion of the number of photons whose energy is less than 120 keV in total photons is 69 percent, and the proportion of energy is 58 percent in the same case. The proportions of simulation result are respectively 70 percent and 65 percent, which are close to the experimental result. The X-ray source can be used for SGEMP simulations and the design method of converter can be used to lower photon energy for other X-ray sources.