The changes in soil use patterns with economic development may lead to the accumulation of heavy metal in soil and then threat food security. Situated at Yangtze Rive Delta (YRD), Zhangjiagang City is an economically developed area. Based on intensive soil sampling from rice-wheat fields and vegetable ones, this paper discussed: (i) the effect of the soil use conversion from rice-wheat rotations to vegetable planting on spatial-temporal distribution of soil heavy metals, such as Cd, Cr, As and Cu, and (ii) the accumulation and pollution trend of soil heavy metals in the current condition with the expansion of vegetable cultivation and the increase of planting years. The results indicated that the concentration of Cd, Cr and Cu in soil were accumulated in the process of vegetable planting except for As. A certain area exceeded the first grade of the national standard for soil environmental quality (background value). If the current trend continued, Cu concentration of 2.4% of soil area would be over the second grade of national standard in by next 10 years, and that of 0.7% over the second grade standard of Cd by next 20 years. Therefore the attention should be paid to the accumulation of soil heavy metals in vegetable fields and potential pollution for the future vegetable planting management.