Because of excessive fertilization，blind fertilization and low fertilizer use efficiency，the study of soil test and formula fertilization index system on Sweet Potato was carried out through a lot of field experiment of fertilizer to guide farmers better for scientific fertilization.This paper illustrated a system, based on the “3414” field tests, that divided soil nutrient content into sufficiency, medium and deficiency grades and established indices to show the degree of sufficiency or deficiency on available N, P and K in soil for sweet potato in Putian. The results indicated that the critical value of sufficiency and deficiency for soil alkali-hydrolyzable N, Olsen-P and available K were 85-128 mg/kg, 10-24 mg/kg and 42-115 mg/kg, corresponding to 75%-90% relative yield of the sweet potato. The recommended fertilizer amount from the fertilizer effect function and the soil NPK test values were exponential regression relation. Obtained from the regression equation, the recommended fertilizer amount of NPK were 114-168 kg/hm2, 51-62 kg/hm2 and 159-323 kg/hm2 under the medium fertility level.