Random field model is adopted for soil permeability, which is decomposed into deterministic trend and stationary perturbation. The KLME method based on the combination of Karhunen Loeve expansion of random field and perturbation analysis is introduced to investigate the effect of continuous and discontinuous trend in log permeability field on statistics of seepage field. The result shows that the distribution of mean and standard deviation of hydraulic head is influenced by the change of trend, which is related to the linear trending direction, the contribution of secondorder correction of mean head and its standard deviation is enhanced with the increase of slope of linear trend, and under the condition of the discontinuous trend, the statistics of hydraulic head presents the irregular spatial distribution.