The invention discloses matrix carrier type slow-release urea based on straw and a preparing method thereof. The matrix carrier type slow-release urea is prepared from 74-97.48 parts of urea, 2.5-20 parts of straw, 0.01-4 parts of polyacrylamide and 0.01-2 parts of ferric salt. The preparing method includes the steps that straw is smashed, and the smashed powder, polyacrylamide and ferric salt are sequentially added into urea melt or mixed and added into the urea melt; the mixture is stirred fully, and mixed slurry is prepared into slow-release urea in different particle sizes. The developed matrix carrier type slow-release urea based on the straw is applied to farmlands, nitrogen volatilization and leaching loss are reduced, the use ratio of nitrogen is increased, a carbon source can be provided for soil microorganisms, microbial activity is stimulated, effectiveness of nitrogen is improved, soil organic matter is increased, and the soil structure is improved. The problems that chemical fertilizer is low in use ratio, crop straw burning causes defaults and the straw is difficult to use are solved. The straw-based matrix carrier type slow-release urea is simple in production process and low in cost and has broad application prospects.