The effects of nano-C—S—H/PCE on the setting time, early hydration and compressive strength of Portland-Sulphoaluminate composite cement were studied. XRD, TG, pH meter and SEM were used to characterize the early hydration products and liquid alkalinity. The enhancement mechanism of nano-C—S—H/PCE on Portland-Sulphoaluminate composite cement was studied. The results showed that the addition of nano-C—S—H/PCE could effectively shorten both the initial setting time and final setting time of fresh composite cement paste. When the C—S—H content was more than 1.0%, the initial time difference of the composite cement was obviously shortened. The nano-C—S—H/PCE accelerated the hydration heat releasing rate of the composite cement, and increased the total hydration heat. The early-age hydration products were increased obviously, however, it had no effect on the type of cement hydration products. The compressive strength of the composite cement mortars at 8 h, 12 h and 16 h were significantly increased.