惯性约束聚变实验对数据测量精度有着很高的要求，诊断设备需要向绝对测量的方向发展，对标定提出了很高的要求。北京同步辐射装置（BSRF）提供了良好的标定光源，其光源特性，如高次谐波份额的数值研究，对标定工作和ICF精密诊断十分重要。通过测量BSRF上4B7B光束线的软X射线源上带有或不带有滤片的标准探测器的电流，研究了不同滤片对单色X射线的透射率曲线，并建立了拟合的理论透射率曲线。根据数据分析，计算出单色光源中二次谐波的比例。实验结果显示，二次谐波在软X射线能段主要集中在180~300 eV以及450~800 eV，所占份额大部分在15%以下，最大可达到25%左右。利用测量的高次谐波份额，开展了对平响应滤片透过率以及X射线二极管灵敏度的修正工作，修正后的结果和理论相符，极大地提高了诊断设备精密诊断能力。完整的理论模型和实验相互验证，说明基于滤片的高次谐波份额测量技术目前已经成熟并且具有广阔的应用前景。

In order to meet the high requirements of the data measurement in the inertial confinement fusion(ICF) experiment, experimental instruments must be developed in the direction of absolute measurement, and the requirements for calibration are also higher. Beijing Synchrotron Radiation Facility (BSRF) provides a good X-ray source for calibration in China. The characteristics of the light source, such as the numerical study of the high-order harmonics content, are very important for the calibration work and the precise diagnosis of ICF. By measuring the current of a standard detector with or without a filter on a soft-X-ray source of beam line 4B7B in BSRF, the transmittance curves of different filters for monochromatic X-ray were studied and a fitted theoretical transmission curve was established. According to this, the proportion of second harmonic in the monochromatic light source was calculated. The results show that the second harmonic in the soft X-ray energy segment is mainly concentrated in the 180-300 eV and 450-800 eV, the share is mostly 15% below, the maximum can reach about 25%. Then, the calibration of the flat-response filter transmittance and the X-ray diode sensitivity was corrected using the calibration results. The revised results are consistent with the theory, which greatly improves the precision diagnosis capability of the diagnostic equipment. The complete theoretical model and experiment results mutual verify, showing that the filter-based technology for evaluating proportions of high-order harmonics is currently mature and has broad application prospects.