The lodging resistance and chemical component contents in culm and leaf sheaths were analyzed by using japonica rice cultivars with different lodging resistance during grain filling. The results showed that there were significant differences in total amount of potassium (K), silicon (Si) and soluble sugars in culm and leaf sheaths, especially total amount of Si.The physical strength and maximum bearing capacity of culm gradually decreased during grain filling, and reached the minimum at the maturity stage, in particular, the physical strength at the dough stage decreased rapidly. The contents and total amount of K and Si in culm and the content of Si in leaf sheaths were increased gradually and presented precipitation phenomenon whereas the content and total amount of K and the total amount of Si in leaf sheaths were decreased gradually and assumed output sign. Except for the total amount of K in culm at the full heading stage, the physical strength was highly significantly and positively correlated with total amounts of K and Si in culm during grain filling, and significantly and positively correlated with the total amount of soluble sugars in culm at the full heading stage and milky stage, with the total amounts of Si and soluble sugars in leaf sheath at the full heading stage and with the total amount of K in leaf sheath at the full heading stage and milky stage. The physical strength was highly significantly and positively correlated with maximum bearing capacity during grain filling. It is suggested that increasing the amount of soluble sugars in plants at the early filling stage, and enhancing amount of Si in plants during grain filling by topdressing Si fertilizer at the early filling stage would be beneficial to improve the lodging resistance of japonica rice.