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作为风机叶片防雷研究过程中的关键物理问题，关于叶片上行先导起始机制及其判据的研究尚待深入。该文利用线电荷和头部点电荷的等效模型模拟雷电下行先导电荷分布，考虑到叶片附近空间电荷的运动、扩散与中和现象，计算了叶片表面电荷密度曲线，发现正电荷集中分布在叶片尖端。利用有限元仿真软件COMSOL计算发现，在雷电下行先导通道内电荷与叶片表面电荷的共同影响下，叶片尖端附近电位发生明显的畸变。基于叶片上行先导发展过程的简化模型，提出了临界长度判据：在叶片尖端上部存在空间背景电势大于流注区域电势的区域，当该区域长度大于临界长度时，稳定连续的上行先导起始。雷电参数(雷电流幅值，下行先导侧面距离等)和风机叶片参数(叶片长度，接闪器半径等)对临界长度无影响；临界长度随空气相对密度、湿度的增加而减小，随海拔的增加而增大。仿真结果与长间隙放电观测数据相符合，验证了该判据的有效性。“,”As a key physical process of lightning protection on wind turbine blades, the inception mechanism and criterion of the upward leader need further. A model of line charge with point charge at the head was used to simulate charge distribution of lightning leader. A curve about surface charge density on blade was plotted after considering the movement, diffusion and neutralization of the space charges, and positive charges was concentrated distribution at the tip of blade. The potential nearby blade was simulated by COMSOL, and it was distorted obviously under the influence of charges in lightning leader and that on the surface of blade. The paper proposed a critical length inception criterion for upward leader based on a simplified model of the development of upward leader. The kernel of the criterion is ‘there exists a certain zone above blade tip where the background potential is larger than that in streamer, and a stable upward leader will incept if the length of this zone is larger than a critical length’. Lightning parameters and blade parameters, such as amplitude of lightning current, lateral distance, length of blade and radius of receptor, have no effect on the critical length. The critical length decreases with the increase of the relative density and humidity of air, and it increases with the increase of altitude. Thefeasibility of the proposed criterion is verified by the observation results of long air gap discharge for the vertical conductors under laboratory conditions.