在反应堆物理-热工耦合过程中，网格划分尺度会影响计算精度和计算时间。利用蒙特卡罗程序和FLUENT程序，对压水堆单棒模型进行不同尺度的网格划分，评估网格划分尺度对耦合结果的影响，得到单个网格中密度差值、温度差值对有效增殖因子和功率分布引入的误差。研究表明当燃料温度差值小于50 K，慢化剂密度差值3 kg/m3时，有效增殖因子相对误差小于10-4，功率相对误差小于1%。使用该规律，对典型的压水堆单棒模型和3×3通道模型进行网格划分并进行耦合计算。结果表明，单棒模型网格总数减少至1/100，计算时间减少至1/4，3×3通道模型网格总数减少至1/50，计算时间减少至1/10，但其结果仍然精确有效。

In nuclear neutronics/thermal-hydraulics coupling analysis, grid size will affect the speed and accuracy of calculation. This paper assesses the effect of the grid size on coupling results by establishing a PWR cell model at different levels of grid size and coupling calculation using the Monte Carlo neutron photon transport code MCNP5, the computation fluid dynamics code FLUENT, and our interface program MF_COUP. The relationship of grid temperature difference, grid density difference, and relative errors of the infinite neutron multiplier and power density distribution are demonstrated. The grid size causes errors less than 10-4 to keff and errors less than 1% to power distribution while the gird temperature difference of fuel is less than 50 K and the grid density difference of moderator is less than 3 kg/m3. Furthermore, a PWR single cell model and a PWR 3×3 cell model are calculated based on our mesh scheme. The results show that the using our mesh scheme is concise and effective while the total number of grid and computation time decrease significantly.