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In order to explore the sustainable effect of onetime application of biochar on the productivity of sloping farmland in black soil area, the threedegree slope farmland runoff plot in the black soil area of Northeast China was taken as the research object, the experimental study was carried out during 2016—2018, two treatments of CK (not applying biochar) and BC (2016, 75t/hm2 biochar, 2017, 2018, no longer applying biochar) were set, and the biochar sustainable effect of land production capacity was analyzed. The improved technique for order preference by similarity to an ideal solution (TOPSIS) model and GM(1,1) model were adopted to calculate and forecast the land productivity index, the results showed that the soil bulk density was decreased significantly (P<0.05) within three years of onetime application of biochar, and the most obvious reduction was 387% in the first year. The porosity, total organic carbon, ammonium N, available P, available K content were increased significantly (P<0.05), 〖JP2〗pH value was significantly increased in the first two years after charcoal application (P2016=0.034, P2017=0.038), and increased by 0.9 and 0.6 respectively, the third year and there was no significant difference in charcoal treatment (P2018=0.067). The application of biochar significantly improved the water holding capacity and soil retention performance of soil, and soil saturation moisture content, field water holding capacity and wilting coefficient were significantly increased (P<0.05), with the maximum growth rates of 558%, 478% and 7.29% respectively, and the annual runoff depth and soil erosion amount were significantly reduced (P<0.05), the maximum annual runoff depth reduction was 492mm, and the maximum soil erosion reduction rate was 5.71%. Soybean yield and water use efficiency were significantly improved (P<0.05), with maximum growth rates of 2901% and 1692% respectively. However, the sustainable effect of biochar on land productivity was weakened year by year. With the extension of biochar application period, the bulk density of BC treatment was increased linearly, the porosity was decreased linearly, and the pH value and total organic carbon were decreased in a power function. Ammonium N, effective P, available K content were decreased linearly, the saturated water content, field water holding capacity and the wilting coefficient were decreased linearly. The annual runoff depth and soil erosion were increased linearly. The soybean yield and water use efficiency showed a power function decline and a linear decrease, respectively. Based on the improved TOPSIS model and GM(1,1) model of grey correlation, the land productivity index was calculated and predicted. The results showed that the BC processed land productivity index was higher than CK, but its value was decreased year by year, and it was very close to CK treatment by 2021. It indicated that the impact of onetime application of 75t/hm2 biochar on land productivity can last for about 5~6 years. The research results can provide a theoretical basis for the application of biochar in the black soil region of Northeast China.