Abstract: The thickness of black soil layer is an important parameter to evaluate the soil quality in Northeast China. To find out its spatial distribution and secular variation, the paper conducts field investigation on the present condition of 61 typical soil profiles from the Second National Soil Survey in the black soil region of Northeast China and analyzes the variation of black soil layer thickness. The results show that the thickness of black soil layer has decreased by 12 cm on average, with the mean thinning rate of 0.32 cm/a in the past 40 years. The thinning thickness of black soil layer in four provinces/regions are significantly different, with the largest thickness and proportion of black soil layer thinning and the most severe ecological risk in Jilin(23.65 cm), followed by Liaoning(11.83 cm), Inner Mongolia(10.33 cm) and Heilongjiang(6.83 cm). There is a remarkable negative correlation between the black soil layer thickness variation and rising temperature in Jilin Province, indicating that with the climate warming, soil organic matter decreases obviously, and also the thickness of black soil layer. In addition, water erosion is also an important factor affecting the thickness thinning of black soil layer. It is suggested the study on black soil thickness determination and spatial mapping be strengthened in the future, which is of great significance to guide the protection and utilization of black land.