In this study, we compared and measured the main physiological characteristics, chloroplast ultrastructure and stem microstructure between dwarf mutant C1056 and wild type CCMC, so as to explore the plant height regulation mechanism of cucumber, excavate new dwarf germplasm, and provide basis for dwarf breeding of cucumber. The results showed that: (1) the mutant C1056 had significantly shorter plant height, darker leaf color, thickened veins, curled leaf tips, wrinkled and shrunk leaves. There was no significant difference in stem diameter, internode number between mutant and wild type, but the internode length of mutant was extremely obviously shorter than wildtype. (2) The stem transverse microstructure showed that the number of mutant vascular bundle was not significantly different from the wild type, while the vessel diameter was reduced. The stem longitudinal section showed that the internode cell became significantly shorter and smaller than that of wild type, while the number of cell was slightly compensated. (3) Compared with wild type, the content of chlorophyll and carotenoid of the mutant both decreased and the ratio of chlorophyll to carotenoid and chlorophyll a/b significantly increased. (4) The chlorophyll fluorescence parameters of mutant did not significantly change. The net photosynthetic rate of the mutant was 8% lower than that of wild type, and stomatal conductance and transpiration rate were 15% and 10% higher than that of wild type, respectively, but the differences were not significant.In mutant, the intercellular CO₂ concentration was significantly higher than that of wild type. (5) The results of transmission electron microscope showed that the mesophyll cell of mutant was smaller than that of wild type, the cell area occupied by chloroplast was significantly larger, and the shape of chloroplast was semicircle and spindle. Most of the stromal and grana layer of abnormal chloroplasts were not obvious, and the stacking was not neat. The results of this study showed that the dwarfing of cucumber mutant C1056 was mainly caused by significantly shortened internode length and smaller cells, and the chloroplast structure of mutant was affected to some extent, but its photosynthetic capacity was not significantly affected.