Granulated blast furnace slag (BFS) powder and fly ash (FA) in industrial waste have become the main admixtures for preparing Portland cement due to their typical pozzolanic properties. Whether recycled brick powder (RBP) and recycled concrete powder (RCP) in construction solid waste can be mixed with BFS and FA to prepare active admixtures is an important way to expand the utilization of multi-source solid waste resources. In this study, RBP, RCP, FA and BFS were used as raw materials to prepare admixtures by wet ball milling. The compressive strength test of binder was carried out with the content of the admixture as the variable, and activity of admixture was evaluated by the pozzolanic specific strength method. The hydration products were analyzed by XRD, TG-DTG, SEM and EDS. The results show that the admixtures prepared from four types of solid waste powders can effectively replace a portion of cement. The compressive strength of cement mortar containing admixtures can reach up to 74.2 MPa at 90 d. Due to the pozzolanic reactivity of RCP and RBP, the diffraction peak intensity of the hydration product CH phase decreases and the C-S-H peak widens after the reaction. Ca2+ and Si2+ in RCP and RBP promote the activation of siliceous and aluminum minerals in FA and BFS. The optimal mass fractions of each component in the active admixture prepared by the synergistic effect of active silicon and aluminum minerals are 15% RBP, 15% RCP, 15% FA, and 5% BFS. The application of active admixtures not only helps improve the utilization efficiency of various solid waste materials, but also helps reduce the dependence of the construction industry on ordinary cement.