X射线能谱分布在双能谱X射线计算层析(CT)成像、CT图像的硬化校正、CT成像的定量分析等方面起着重要的作用。传统的X 射线能谱估计方法是通过直接测量X射线穿过不同厚度物质后的衰减数据，间接估计X射线的能谱分布。与传统方法相比，提出一种由已知结构模体的CT数据间接估计X射线能谱的方法。该方法的特点是：1)不需要精确测量射线穿过物质的长度，只需要对已知结构和材质的模体进行CT扫描便可获得该材质下的衰减曲线，并且该方法对模体的制作精度要求不高；2)采用了带非线性约束的迭代求解方法，由于在迭代求解过程中加入了X射线能谱模型作为约束条件，大大减轻了求解模型的病态性和不适定性。所采用的X射线能谱模型考虑了靶材料对射线的吸收，更加接近实际CT系统的X射线能谱分布。数值实验表明：与已有方法相比，该方法能够更精确、更稳定地估计出X射线能谱的轫致辐射分布和特征辐射分布。

X-ray spectrum plays an important role in dual spectral X-ray computed tomography (CT) imaging, CT beam hardening correction, quantitative CT analysis and so on. The conventional methods estimate the spectrum from a set of transmission data measured directly for different thicknesses of step-wedge phantoms. A novel estimation method of X-ray spectrum is proposed. The proposed method has two features. First, the dependence of the transmission intensity on the thickness of attenuation materials from the CT data of simple phantoms is restored. This not only simplifies the phantom production and the measurement process, but also can restore a more accurate dependence of the transmission intensity on the thickness of materials. Second, an alternative iteration algorithm for the spectrum estimation based on the parameter spectrum model is developed, in which the effect of the anode material is considered. The algorithm can relieve ill-posedness and instability for solving the spectrum estimation problem, by using the parameter X-ray spectrum model as constraint condition. The results of numerical experiments with several simulation data suggest that the proposed method is capable to reconstruct X-ray spectra more accurately and robustly for both bremsstrahlung and characteristic photons, compared with some transmission measurement methods.