The very slow polymerization rate of alkali-activated fly ash (AAFA) cementitious material at room temperature cannot meet the setting and hardening requirements of on-site construction. In this paper, AAFA was prepared with ultra-fine fly ash at room temperature, and its flow performance was optimized by superplasticizer. The results showed that the AAFA paste prepared by replacing original fly ash with 50% ultra-fine fly ash exhibited the characteristics of rapid setting and high early strength at room temperature, and its initial setting time was 42 min, and the compressive strength at 3d was 9.1 MPa, while cannot flow with w/b at 0.35. Naphthalene superplasticizer enhanced the dispersion of fly ash particles in AAFA paste, significantly reduced the apparent viscosity, and thus improved the initial fluidity and fluidity retention of the paste, but encapsulated the fly ash particles and weakened the connection between the gel products, thereby prolonging the setting time of the AAFA paste and unfavorable to the compressive strength of the early age. Naphthalene- melamine composite superplasticizer also significantly reduced the initial apparent viscosity of AAFA paste and improved its initial fluidity. However, due to its influence on the polymerization process, the fluidity loss of AAFA paste was accelerated and the development of compressive strength was promoted.