The soil properties of embankment slope filled with cement solidified dredged sludge commonly feature high variability. Meanwhile, in construction process of cement-mixed embankment, horizontal drainage plate is generally used to accelerate the consolidation of cement-mixed soil, which makes the soil strength show a spatial distribution trend at the vertical direction (perpendicular to the drainage plate) after the primary consolidation finished. The traditional stationary or quasi-stationary random field model cannot well characterize this trend. This paper proposes a non-stationary model to characterize the attenuation trend of soil strength along the normal direction of drainage plate. The strength reduction method and Monte Carlo simulation are combined to evaluate the reliability of slope, and the proposed model is compared with two existing models (i.e., traditional stationary random field model and depth trend non-stationary random model). The influence of different random filed models on safety factor and slip surface are investigated, and the impact of trend parameters in the proposed model on slope reliability are discussed. The results show that the stationary random field model and depth trend non-stationary random field model may overestimate the reliability of embankment slope, and the proposed non-stationary random field model can consider both the trend term and random fluctuation term in vertical direction and the attenuation trend in normal direction of drainage plate, which is in good agreement with the existing research.