Abstract: Diurnal variation of photosynthesis characteristics of two germplasms （Z110 and Z132） of Zoysia japonica which had different long term water use efficiency and its mutual relationship and environmental factors were studied with Li\|6400XT photosynthesis system. The results showed that net photosynthetic rate and stomatal conductance of Zoysia japonica presented double\|peak curve，with the peaks appearing at 11：00 and 15：00，net photosynthetic rate appeared a typical phenomenon “photosynthesis midday depression”; The diurnal variation of inter\|cellular CO2 concentration presented a concave one\|peak curve in the leaves of Zoysia japonica，and the lowest peak of inter\|cellular CO2 concentration was observed at 13：00; The diurnal variation of transpiration rate presented a raised one\|peak curve in the leaves of Zoysia japonica，and the peak of Z110 and Z132was observed at 12：00 and 11：00， respectively; Momentary water use efficiency and potential water use efficiency presented irregular changes. Relationships between environmental factors and photosynthesis characteristics were not equal in two germplasms of Zoysia japonica.

Key words: Zoysia japonica, photosynthesis characteristics, diurnal variation, environmental factors, relationships