Controlled low strength materials (CLSM) were prepared by using different proportions of ground granulated blast furnace slag (GGBS) and fly ash (FA) mixed with sandy soil and decoration wastes. This paper studied the influences of GGBS and FA dosages on the fluidity, bleeding rate, setting time and compressive strength of CLSM. The effects of GGBS and FA dosages on the phase composition and micromorphology of CLSM were explored by XRD and SEM. The results show that with the increase of GGBS and FA in CLSM, the bleeding rate decreases, and the setting time shortens. When FA dosage remains unchanged, and GGBS increases from 150 g to 270 g, the 3 d compressive strength of CLSM increases from 2.01 MPa to 4.00 MPa, and the 28 d compressive strength increases from 6.83 MPa to 11.12 MPa. When GGBS dosage remains unchanged, and FA changes from 120 g to 240 g, the 3 d compressive strength increases from 2.41 MPa to 3.13 MPa, and the 28 d compressive strength increases from 6.65 MPa to 10.24 MPa. GGBS and FA increase the compactness of CLSM as more calcium silicate hydrate (C-S-H) and calcium silicaluminate hydrate (C-A-S-H) are produced.