Geological high background values and arsenic contamination from industrial and mining industries are the prominent environmental problems of soil heavy metal contamination in China and Southeast Asia. Airborne vegetable with the relatively easy uptake and accumulation of arsenic is the main year-round leafy vegetable and risk source of arsenic exposure in these regions. Moisture and fertiliser affect the translational transport and accumulation of arsenic in the soil-crop system, but information on the effects of water and fertiliser control on the growth and arsenic accumulation of multi-cropped mowed water spinach in mild-to-moderate arsenic-contaminated vegetable plots is not yet clear. Therefore, in this experiment, a high-yielding variety of large-leafed water spinach, which is widely grown in actual production, was selected, and urea (Urea), urea peroxide (UHP), and organic fertiliser (OF) were applied under water management of flooding (WF) and alternating wet and dry (AWD), respectively. Three consecutive above-ground edible young stems and leaves of each treatment of the water spinach were mowed for three consecutive crops during the 178-day potting experiment, to explore the effects of the water spinach on the Arsenic accumulation and the effect of arsenic transport and transformation in soil. The results showed that different combinations of water and fertiliser and the number of mowing significantly affected the yield and arsenic accumulation in water spinach. Increasing the number of mowing increased the above-ground biomass of third-crop water spinach under WF conditions by 11.23%—51.61% compared with the first crop, the total arsenic content was significantly reduced by 57.24%—94.43%, and the ability of water spinach to transport arsenic was reduced by 2.4—18.05-fold; the arsenic accumulated in the above-ground of AWD—Urea and AWD—UHP treatments at the time of the third crop was lower than the national food safety limit standard, achieving safe production. In conclusion, when planting water spinach in moderately arsenic-contaminated vegetable land, it is recommended that the first three crops are planted in WF—OF mode with remediation as the main line; and after mowing the three crops, it is safe to produce under AWD—UHP or AWD—Urea conditions. This study clarified the effects of water and fertiliser management and the number of mowing on the accumulation of arsenic in water spinach, and provided theoretical references for the remediation of mildly to moderately arsenic-contaminated vegetable land.