Abstract: Composite materials with the property of slowly releasing urea had been prepared by using lignin and clay as starting materials in this research. SEM pictures of lignin/clay composite material prepared showed that sphere-like assembling structure of lignin had been transferred into honeycomb assembling structure with more pores for hydrogen bonding between hydroxyl groups of both of the starting materials. Leaching experiments confirmed that the prepared lignin/clay composite materials with the porous structure owning a function of slow releasing property for urea molecules, and the weight ratio of m(lignin):m(clay):m(urea)was 2:1:4 in the composite. Also, what had been confirmed experimentally was that the addition of polyvinyl alcohol as filmogen could improve the slow releasing properties of lignin/clay composite materials for urea molecules. Water adsorption experiments showed that the lignin/clay composite materials prepared could adsorb the water in air, which was helpful for promoting dry soil to keep their water. Soil urease activity inhibition experiments showed that the prepared composite materials could reduce urease activity which could transfer urea into volatile ammonia. Specially, when copper ions were introduced into between layers of clay of composite materials, the prepared lignin/clay composite materials inhibited urease activity more seriously in soil.