Abstract: The loess belongs to the unsaturated soil, and has the geological characteristics, such as macro pore, vertical joints growth, wet collapsibility, etc. It makes the geological disasters occur frequently, seriously restricting the economic development in the loess area. Because the loess has water sensitivity, the water factors are the main factors for geological disasters. The change of soil suction matrix is the important factor for slope stability. The paper uses the filter paper method to study unsaturated loess matrix suction, the result shows the matrix suction gradually decreases with the moisture content increase. The matrix suction is more sensitive when the soil moisture content is smaller. Moisture content is higher, the change of the matrix suction is smaller; When the water content reaches saturation, the matrix suction disappears; and the soil shear strength gradually decreases with the increase of moisture content. It is considered that the filter method is a relatively simple and convenient. Through the research., the filter paper method has strict requirement on around air in the operation process, is a quick, easy test method for the matrix suction of unsaturated soil.