Recycled fine powder (RFP) is difficult to be effectively utilized due to its low activity, resulting in a great waste of resources. To stimulate the activity of RFP, the effects of traditional alkali activators (sodium hydroxide, calcium hydroxide, magnesium hydroxide, sodium silicate), alcohol amine activators (polyisomeric alcoholic amine, triethanolamine) and nanocrystalline nuclear activator on the compressive strength of mortars mixed with RFP were investigated. Meanwhile, the effects of chemical activators on the hydration heat release, hydration products and microstructure of RFP-cement pastes were analyzed to reveal their promotion mechanism. The results show that sodium hydroxide and sodium silicate can further reduce the compressive strength of mortars mixed with RFP, and the relationships are linear inverse with their dosage. Calcium hydroxide, magnesium hydroxide, triethanolamine and nanocrystalline nuclear activator can improve the early strength under certain dosage conditions, but can not improve the later strength. Polyisomeric alcoholic amine can significantly improve the compressive strength of each age through promoting the hydration of mineral phases tricalcium aluminate (C3A) and tetracalcium aluminoferrite (C4AF), accelerating the hydration process of RFP-cement pastes, improving the compactness of the interfacial bond between cement matrix and sand. The activity index of RFP increases from 62.8% to 74.8% at the optimal dosage of 0.2% (mass fraction). The research results can provide reference for improving the utilization rate of RFP and achieving the goal of energy conservation and emission reduction in the construction industry.