The Pinus tabulaeformis plantation of severely burned areas in Beijing was taken as the research object, based on in situ sampling method and indoor immersion method, litter samples were collected in control plot and burned plot from July 2020 to December 2020 and their standing crops, water holding capacity and effective retention were measured and analyzed to explore the decomposition and hydrological effects of litter under the interference of forest fire. It could provide a basis for giving better exerting the function of forest water conservation and soil and water conservation. The results showed that: (1) The average standing crop of litter in semi-decomposed layer and decomposed layer of Pinus tabulaeformis plantation were 16.18 t/hm² (leaves proportion > 80%) and 31.88 t/hm², the average thickness were 2.77, 2.79 cm, respectively. Compared with the control plot, the litter thickness and standing crop of the semi-decomposed layer after fire were decreased by 39.35% and 53.77% respectively. (2) The average natural moisture content of litter in semi-decomposed layer (41.94%) was slightly higher than that in decomposed layer (36.07%) in Pinus tabulaeformis plantation, and the average maximum water holding capacity was 201.88%, which was lower than that of decomposed layer from July to September, and vice versa from October to December. The average maximum water holding capacity and effective retention in semi-decomposed layer were 35.80, 19.85 t/hm², which were significantly (P < 0.05) lower than those of decomposed layer from August to December (69.28, 46.64 t/hm²). Compared with the control plot, the natural moisture content, maximum water holding rate, maximum water holding capacity and the effective retention of litter in semi-decomposed layer after fire were decreased by 32.19%, 13.36%, 60.05% and 62.47% respectively. (3) In the 24-hour immersion process, the litter water holding capacity and water absorption rate in semi-decomposed layer were lower than those of decomposed layer from July to September, and vice versa from October to December. The water holding capacity and water absorption rate of litter after fire in semi-decomposed layer were lower than those in control plot. In conclusion, the decomposition of litter (semi-decomposed layer) in Pinus tabulaeformis plantation was first fast and then slow, and the decomposition was accelerated after burning. The indexes of water holding capacity and water holding processes of litter mainly showed that decomposed layer was higher than semi-decomposed layer, and non-burned was higher than severe burned, that is, the hydrological effects of litter was affected by the decomposition stage and burning.