In this paper, armed at the shortage of domestic agricultural controlling equipments, combined with the current Chinese made fertilizer equipment, introduces an automatic controller of variable rate fertilizer applicator which suitable domestic food-producing area to promote and use. The automatic controllers of variable rate fertilizer applicator can fully automatic intelligent control the agricultural machinery and equipment. Agricultural workers only need to input the operation parameters to achieve the aim of automatically variable rate fertilization. Automatic controller of variable rate fertilizer applicator can also connect GPS controller to achieve fully automated variable rate fertilization. Paper on controller introduced the hardware and software design in detail, and carried out experiments and tests. Through field experiments and tests show that automatic controller of variable rate fertilizer applicator can achieve the purpose of precise variable rate fertilization.