The use of waste rock as an aggregate in mining backfill is environmentally friendly and cost-saving. The backfill slurry flow property varies with the change in aggregate, binder content, solid concentration, and additives. The slurry flow in a pipeline is governed by its properties, which makes it crucial to study the flow properties and their effects. One example is a fly ash-waste rock mixed slurry in Jinchuan Nickel, China. Tests on the slump, slump flow, mortar consistency, layering degree, and bleeding rate are performed to reveal the effects of the slurry concentration, binder content, and fly ash addition on the flow properties. Those relations are analyzed, and two new indices are derived (F₁ and F₂) using the principal component analysis method. Finally, the application results show that F₁ > 0 indicates a nonhomogeneous flow; F₁ < 0 and F₂ > 0 indicates a high-density slurry flow; F₁ < 0 and F₂ < 0 indicates a paste slurry flow.