抛弃式温度深测量仪（XBT）可标定海洋深度剖面的水文数据，XBT探头运动深度的准确校订关系到系统的精度。本文基于非线性水动力理论和大涡模拟计算方法，建立等比例三维CFD数值模型和水动力非线性运动方程，数值分析探头的外流场特征，以阻力系数为边界条件求解深度的解析解，进行探头入水线速度实验测定，验证深度解析解的拟合准确性。结果表明：数值模型计算的阻力系数误差小于4.39%，XBT探头的阻力来源于头部滞止区和中段逆向压差流动。以阻力系数为边界条件可推导二阶微分运动方程（FRE方程)，FRE方程的双曲反正切解析解与试验测定值的最大速度偏差为6.2%，距离偏差为3.2%，误差可控。该方法可为XBT探头的设计和工程应用提供准确的速度和深度参考，为数字化集成该型产品提供基础，提高深度标定的准确性。

The expendable bathythermograph (XBT) is capable of measuring hydrological data across ocean depth profiles， so the precision of the XBT probe's operational depth is crucial to the system's accuracy. Based on nonlinear hydrodynamic theory and integrated with large-eddy simulation methods， this paper establishes a scaled three-dimensional computational fluid dynamics (CFD) numerical model and nonlinear hydrodynamic motion equations. Through numerical analysis of the probe's external flow field characteristics， the drag coefficient is extracted and utilized as a boundary condition to solve for the solution which can estimate the motion depth. Experiments conducted to verify the accuracy of the motion depth estimated. The results reveal that the error in the drag coefficient calculated by the numerical model is less than 4.39%. The drag on the XBT probe originates from the stagnation zone at the head and the adverse pressure gradient flow in the middle section. Using the drag coefficient as a boundary condition， the second-order differential motion equation， known as the nonlinear falling equation (FRE)， can be derived. The hyperbolic arctangent analytical solution of the FRE exhibits a maximum velocity deviation of 6.2% and a distance deviation of 3.2% compared to experimentally measured values. This methodology provides accurate speed and depth references for the design and engineering application of XBT probes， laying a foundation for the digital integration of this type of product and enhancing the accuracy of depth calibration.