The flow characteristics of granular materials and gas in a vertical packed moving bed, called a "stand pipe", furnished at the bottom of the fluidized bed are investigated theoretically and experimentally. A correlation equation of axial stress sigma(z) and voidage epsilon of granular materials in the stand pipe is proposed through investigations of the continuity equation, the momentum balance equation, Ergun＇s equation for gas pressure loss and the gas pressure distribution data measured experimentally in the axial direction. Regarding the relation of the axial stress and the voidage, it was recogniged that: 1. The absolute value of d sigma(z)/d epsilon is large at the voidage near the minimum fluidizing condition, and at the voidage in the dense packed condition, and an inflection point of a exists in range between the both conditions; 2. It seems to be the wall-friction-effect of stand pipe that the absolute value of d sigma(z)/d epsilon is larger at the inlet of stand pipe, and; 3. The stress is also a function of the particle diameter. The gas flow rate, axial stress distribution of granular materials, gas pressure distribution and voidage distribution in the axial direction of the stand pipe can be calculated from relating equations.