On fine days，daily dynamics of photosynthetic characteristics in four alfalfa varieties under dry farming conditions were monitored using Portable LI-6400 Photosynthesis System. The four alfalfa varieties included Xinjiang big leaf, Ameristand 201, Amerigraze 401 and Lobo, which were at the flowering stage after the first cutting in their fourth year of growth. The results were summarized as follows: ① The curves of diurnal variation in Pn, Tr and Gs of four alfalfa varieties leaves had two peaks, and an obvious midday depression at 12:00 o’clock, although there were differences in the time and the value of the peaks occurred in terms of Pn, Tr and Gs. WUE had two peaks in all the varieties except in Lobo, and the four alfalfa varieties all reached the highest value of WUE at 8:00 o’clock. ②Based on the tendency of changes in Pn, Ci, Ls, it was speculated that the midday depression in the alfalfa varieties was controlled by stomatal factor. ③Daily average values in Pn, Tr and WUE of Ameristand 201, Amerigraze 401 and Lobo were higher than Xinjiang big leaf, with Ameristand 201 being the best. ④ Correlation analyses showed that the factors affecting Pn could be ranked, from the highest to the lowest, as PAR>Gs>RH>Ta>VPD, and the factors affecting Tr could be ranked as PAR>RH>Ta>>Gs>VPD.