•Influence of mixing time on chemical and physical environment of paste was assessed.•Mixing time has significant effect on the property of paste.•Mixing action greatly accelerates the hydration kinetics in the acceleration period.•Excessive mixing reduces the UCS in 28 days of curing. Mixing is a crucial step in the application of any cement-based material. To have a clear understanding of the effect of mixing on cemented paste backfill (CPB) properties is necessary for the preparation of high-quality CPB. This paper researches the effect of mixing time on fresh and hardened properties of CPB, such as hydration kinetics, mechanical property, micro-structural characterization, and ion elution by using inductively coupled plasma mass spectrometry (ICP). The results show that the hydration kinetics and mechanical property of the CPB are sensitive to the mixing time. The mixing time mainly affects the acceleration period, and an improved shearing condition is beneficial to the improvement of the mechanical strength of CPB, especially the early strength, while excessive mixing causes deterioration to mechanical property. These observations can be explained by changes in physical and chemical composition of fresh state CPB due to different mixing programs.