Experiments of performance test, sand column leaching, rainfall simulation and indoor soil training test under different field moisture capacity were carried out to study the material characters and mechanism of nitrogen leaching of slightly-water-soluble felted and coated fertilizer applied under the semi-arid conditions. It showed that water soluble coated material was compact by 27.52 g/(m2•h) for its permeability and had certain biodegradable characters. Compared to urea, slightly-water-soluble felted and coated fertilizer has an obvious slow-release effect and may release certain amount of nitrogen with rainfall or irrigation in time and 8.5% field capacity is a lower limit for nitrogen releasing. Its preliminary results of slight water solubility have been reflected.