基于Longuet－Higgins提出的非线性随机海浪模型，在二阶近似下通过直接计算联合分布的各阶矩，导出了非线性海浪波面高度和波面垂直速度的联合分布。该分布为非正态，其形式为截断的级数，而非由累积矩母函数方法可能得到的渐近无穷级数。由于非线性的影响，波面高度与波面垂直速度不再相互独立。 Based on the non-linear stochastic ocean wave model proposed by Longuet-Higgins, the joint distribution of nonlinear wave height and vertical velocity is derived by directly calculating the moments of the joint distribution under the second-order approximation. The distribution is non-normal, in the form of truncated series, rather than the asymptotic infinite series that may be obtained by the cumulative matrix function. Because of the non-linearity, the wave height and the wave velocity are no longer independent of each other.