Agricultural plastic mulch films are a major source of plastic pollution of croplands. In China, which uses about 68% of the plastic mulch film produced globally (ca. 1.4 million tonnes y^-1), soils have been heavily contaminated with mulch fragments. Here, we collected a national dataset of macroplastic residues (> 5 mm) in soil, including 3145 sampling sites, and provincial plastic film usage from 1992 to 2019 in China, and we established a linear model between the residue amount and historical cumulative usage within each province. We quantified the amount of plastic mulch residues in Chinese croplands on a national scale during the past 30 years and predicted plastic pollution until 2050. Our results reveal the total national amount of plastic mulch residue in 2020 to be 2.07 million tonnes with a 95% CI of [1.67, 2.58]. This accumulated amount of plastic in Chinese soils roughly equals the annual amount of plastic films used globally (2.08 million tonnes in 2018), which is about 8% of the national historical used plastic mulch film (27.3 million tonnes) remains in soil as legacy plastic. Plastic concentrations in Chinese croplands range from 7.7 kg ha^-1 in Anhui to 399 kg ha^-1 in Xinjiang, with an average value of 119 kg ha^-1 (equivalent to 0.03 g kg^-1 soil). We predict that the total amount and average concentration of plastic residues in Chinese croplands will reach 6.24 million tonnes and 357 kg ha^-1 (equivalent to 0.1 g kg^-1 soil) in 2050 under current plastic usage. There is an urgent need for regulatory actions to control plastic pollution in Chinese agriculture.