The artificial forests in the Pingshuo open-pit coal mine area have shown varying degrees of decline after 20-30 years of establishment, and litter plays an important ecological role within these forests. It is urgent to understand how the hydrological characteristics and nutrient return potential of litter respond to this decline. This study focuses on the litter from Robinia pseudoacacia pure stands and mixed stands of Robinia pseudoacacia and Ulmus pumila in the Pingshuo mining area, examining different severities of forest decline in terms of quantitative characteristics, water-holding capacity, and contents of carbon (C), nitrogen (N), phosphorus (P), and potassium (K) as well as their potential for nutrient return. The results indicate that the accumulation of litter in the heavily declining mixed forest is significantly 49.4% more than that in the normal forest (P < 0.05). As the severity of decline increases, the maximum water-holding capacity of litter from both types of forests generally shows an upward trend, with the rate of water absorption decreasing rapidly initially and then slowing down later; the litter from the mixed stands of Robinia pseudoacacia and Ulmus pumila has a higher maximum water-holding capacity, maximum water-holding rate, and overall water-holding rate than that from the Robinia pseudoacacia pure stands. The C content in the mixed stands of Robinia pseudoacacia and Ulmus pumila is 2.11 times that in the Robinia pseudoacacia pure stands.In pure forests, the N and K content in heavily declining forests increased significantly by 0.9% and 0.13%, respectively, compared to normal forests ( P < 0.05). In the mixed stands of Robinia pseudoacacia and Ulmus pumila , heavily declining forests showed a significant increase in P and K content of 0.07% and 0.04%, respectively, compared to normal forests ( P < 0.05). There are significant differences in the potential return amounts of C, N, and K nutrients among different forest stands and degrees of decline ( P < 0.05). In summary, the decline in the mining area"s artificial forests enhances the water-holding capacity and nutrient return potential of their litter, which is beneficial for the improvement of degraded forest lands, and the mixed stands of Robinia pseudoacacia and Ulmus pumila appears to have a relative advantage.