Using organic fertilizer, water-retaining agent (polyacrylamide PAM, polymer water-absorbent resin SAP and Water) as test materials, the effects of organic fertilizer combined with water-retaining agent on water infiltration and nitrogen leaching of purple soil were studied through indoor soil column simulation test. The results showed that organic fertilizer combined with water-retaining agent could effectively increase soil water and fertilizer retention capacity, and was an effective measure to control soil water and nutrient leaching. Single application of organic fertilizer and application of organic fertilizer combined with water-retaining agent both could reduce the wetting front migration depth and infiltration rate. Compared with the control, the wetting front migration depth of the above two treatments decreased by 33.33%~46.49%, the infiltration rate decreased by 22.73%~31.82%, and the cumulative leaching solution volume decreased by 1.25%~6.78%. The application of organic fertilizer had a certain fertilizer-preserving ability, but the fertilizer-retaining capacity gradually decreased with the increasing of leaching times. Compared with the control, the cumulative loss rates of nitrate nitrogen and total nitrogen increased by 12.00% and 17.51%, respectively, under continuous leaching. Organic fertilizer combined with water-retaining agent could effectively reduce nitrogen leaching amount and nitrogen leaching rate, and improve soil fertility retention capacity. Compared with the application of organic fertilizer, the nitrate loss rate and the total nitrogen loss rate of organic fertilizer combined with water retention agent treatment decreased by 35.49%~78.46% and 35.53%~71.85%, respectively. Among them, organic fertilizer combined with PAM had the best effect of water retention and fertilizer retention.