Abstract: Abstract: This study investigated the resistance of rice stem to lodging, and physical and chemical properties of rice culm of different rice varieties under high-yielding cultivation condition in mechanical transplanting with small seedling. Four representative rice varieties were used including indica-japonica hybrid riceA, japonica hybrid rice B, conventional japonica rice C, and indica hybrid rice D as materials. The stem morphological and mechanical traits were analyzed. The results showed that: 1) Compared with B, C, and D, A had higher value of breaking resistance and bending moment, and the lodging index of A was lower than that of D, but higher than that of B and C; 2) In terms of stem structure characteristics, the loading force, springiness, cohesiveness, flexural rigidity, fracturability, hardness, puncture strength, and firmness of basal internode were higher for A than B, C, and D; 3) Plant height, panicle height, gravity center height, internode diameter, stem cross-sectional area, culm wall cross-sectional area, total area of vascular bundles, area of big and small vascular bundles, the number of big and small vascular bundles of A were the highest among the 4 rice types, but the stem type index, the relative area of culm wall cross-sectional, big vascular bundles, small vascular bundles of A were lower than those of B and C, and higher than those of D; 4)The content of soluble sugar, starch, cellulose, lignin, K, Si, Ca, Cu, zinc and other chemical composition in stem and sheath of A were lower than those of B and C, but higher than those of D; Chemical components such as N, Mg, Fe, Mn content of A were higher than those of B and C, but less than those of D; 5) Correlation analysis showed that the lodging index was significantly (P<0.05) positively correlated with gravity center height, culm diameter, cross-sectional area, and highly significantly positively (P<0.01) correlated with relative weight height, culm length, N, Mg, Fe and Mn content, but significanty (P<0.05) negatively correlated with starch and Cu content，and highly significantly (P<0.01) negatively correlated with stem type index, relative stem wall area, the relative area of vascular bundle, and the content of soluble sugar, cellulose, lignin, K, Si, Ca and Zn. Therefore, the resistance of stem to lodging for indica-japonica hybrid rice of Yongyou series under mechanical transplanting condition was better than that of indica hybrid rice, but inferior to that of hybrid japonica rice and conventional japonica rice. Differences in physical and chemical characteristics of culm were closely related with lodging resistance in rice. The study provided a theoretical and technical support for the mechanization and lodging resistance cultivation of indica japonica hybrid rice in the lower reaches of the Yangtze River.