Ability of intercepting and utilizing sun light for growth and dry matter accumulation are key traits for a maize line, thus the combining ability of a maize line on photosynthetic traits is very important information for maize breeders to set goal in a breeding program, especially in a hybrid breeding program. However, little studies had been done on the combining ability for maize photosynthetic traits such as light-saturation point (LSP), light component point (LCP), apparent quantum efficiency (AQE), maximum Photosynthesis (Pmax), the activity of ribulose-1,5-bisphosphate carboxylase (RUBP) and phosphoenolpyruvate carboxylase (PEPC), which are key photosynthesis enzymes. In this paper, the general and specific combining ability for maize LSP, LCP, AQE, Pmax, RUBP and PEPC activities, and soluble protein content (Pro) were studied via a six-parent diallel design. The results showed that, firstly, the Baker’s ratios of 2GCA MS/(2GCA MS + SCA MS) (GSR) for LSP, LCP, PRO, Pmax, AQY, RUBP, and PEPC were 0.89, 0.77, 0.84, 0.68, 0.41, 0.62, and 0.97, respectively. These results indicate that additive gene effects were more important than non-additive gene effects in controlling PEPC, LSP, PRO, LCP, Pmax, and RUBP. Thus for a breeding program aiming at these five traits, an inbred line with higher positive GCA effect should be used. Secondly, Material effects for PRO, RUBP, LCP, and Pmax and non-material effects for AQY, LCP, PRO, PEPC, and RUBP were significant. Thus when these traits are for breeding goals, it should be considered which line should be used for female and which line should be used as male parents. Finally, it was found that relationships among these traits from parent lines are different from those among crosses made from their parent lines. In addition, correlation between LCP and Pmax is significantly positive and correlation among LSP and RUBP, PCP and PEPC are significantly negative.