The fluidity of fly ash-based shotcrete material plays a very important role in practical engineering applications. In order to explore the regulation mechanism of water reducing agent on the fluidity of fly ash-based slurry, the effects of different water reducing agent dosage on slurry flow performance were compared through the characteristics of reducing water rate, fluidity, setting time, slurry viscosity and shear stress，and the best water reducing agent and dosage were selected. The change law of hydration process and time of flyash-based slurry by polycarboxylate acid superplasticizer (PCE)was emphatically explored by using hydration heat analyzer, X-ray diffraction and scanning electron microscope and the hydration mechanism of shotcrete materials with PCE was proposed. The results show that PCE has the most obvious improvement on flow performance of fly ash base slurry. When the saturated content is 0.6%, the water reduction rate can reach 29.3%, the fluidity extends from 113 mm to 351 mm, the initial setting time is extended from 32 min to 149 min, and the final setting time is extended from 42 min to 182 min, with a significant delayed setting phenomenon. In the early hydration process, The adsorption of PCE can inhibit the dissolution of C3A, hinder the growth of ettringite (AFt) and change its crystal form. At the same time, the complexation of PCE can combine with Ca2+  to form complex, affecting the formation of Ca(OH)2, delaying the enrichment of Ca2+ and prolonging the induction period of cement hydration. The hydration of C3S is also inhibited, which reduce the number of C-S-H nucleation and the second hydration exothermic peak. In the middle and late stages of hydration, the inhibition effect of PCE fails and the mechanical strength of the material increases gradually. PCE can only delay the early hydration process, but has no effect on the middle and late hydration process.