With weak gluten wheat Yumai 50 as test material, this paper studied the sucrose accumulation in flag leaf and starch accumulation in kernel under effects of nitrogen, phosphorus and potassium fertilization. The results showed that nitrogen and potassium fertilization increased the sugar content in flag leaf at early and late filling stage, respectively, while phosphorous fertilization had little effect. Nitrogen, phosphorous, and potassium fertilization increased the sucrose-synthase activity in flag leaf, but the effect differed with time, i. e., at mid filling stage for nitrogen fertilization, early filling stage for phosphorous fertilization, and early and mid stage for potassium fertilization. As for the sucrose phosphate-synthase activity in flag leaf, it was increased by nitrogen fertilization in 24 days after anthesis, by potassium fertilization at early and mid filling stage, and by phosphorus fertilization at late filling stage. Nitrogen, phosphorus and potassium fertilization increased the sugar and starch contents in kernel, and the effect of potassium fertilization was most significant. Phosphorus fertilization increased the accumulation of amylose, while potassium fertilization improved that of amylopectin in kernel.