目的　提出一种用于描述高能X射线中心轴剂量特性的数学模型 ,并且给出一种用于计算临床组织模体比 (TPR)表的方法。方法　分别对 6、18和 2 4MVX射线的实测TPR数据与深度和照射野之间的关系进行二阶指数线性回归分析 ,推导出描述TPR值随深度和照射野变化的数学模型。通过对模型的计算结果与实测数据之间的误差分析来评价模型精度 ,并给出确定模型参数所需的最少实测数据。结果　只需 8个TPR数据即可确定由 5个参数构成的二阶指数模型 ,其参数均与辐射质指数线性相关。对应 6、18和 2 4MVX射线 ,使用该模型计算的TPR数据表与实测表的误差分别在 1.5 %、1.2 %和 1.1%之内。并可同时求得描述原射线中心轴剂量特性的 2个主要指标 :衰减系数 (μ)和硬化系数 (η)。 结论　该模型建立了一种从有限实测数据得出临床TPR数据表的有效方法 ,可用于对X射线中心轴剂量特性的数学描述 Objective To propose a mathematical model for describing the dose characteristics of high-energy X-ray central axes, and to provide a method for calculating clinical tissue motif ratio (TPR) tables. Methods The second-order exponential linear regression analysis was performed on the relationship between the observed TPR data of 6, 18, and 24MV X-rays and the depth and field. The mathematical model describing the change of TPR value with depth and radiation field was deduced. The accuracy of the model is evaluated by the error analysis between the calculated results of the model and the measured data, and the minimum measured data required to determine the model parameters are given. Results Only eight TPR data can be used to determine the second-order exponential model consisting of five parameters whose parameters are linearly related to the radiation quality index. Corresponding to 6, 18, and 24MV X-rays, the error between the TPR data table and the measured table calculated using this model is within 1.5 %, 1.2 %, and 1.1 %, respectively. At the same time, two main indexes describing the dose characteristics of the central axis of the original ray are obtained at the same time: attenuation coefficient (μ) and hardening coefficient (η). Conclusion This model establishes an effective method for obtaining clinical TPR data tables from limited measured data and can be used for mathematical description of X-ray central axis dose characteristics.