In this work, the four flow regimes of powders, i.e., bubbleless regime, bubble regime, plug regime and now stopping regime, in hoppers connected to a moving-bed standpipe with negative pressure gradient were observed by analyzing the signal of instantaneous pressure fluctuation and measuring average solids flow rate. The effect of the size of the orifice of a hopper, the half-angle of conical hopper, and the properties of powders on the regime and average solids flow rate were discussed in detail. Based on the properties of fluidized powders, the boundary of regimes and a correlation to predict the average solids flow rate are presented.