This paper describes experimental research on the wall normal stress in a laboratory-scale coal silo. The stresses were measured during discharge by pressure sensors arranged in the wall of the silo. The results show that the wall normal stresses at the upper part of hopper remain fairly constant for about three-fourths of the discharge, and then oscillate violently. The dead zone and the saturation effect of pressure in silo contribute to the smoothness and steadiness of those stresses in the stable stage of discharge. A tentative procedure is proposed to predict the funnel flow pattern of which the lower merge point has some distance from the edge of the outlet. Furthermore, a large fluctuation traveling upward from the outlet was detected during the initial discharge period. The movement of the lower merge point, which changes the flow pattern and stress state zone, is reasonably responsible for the large fluctuation. (C) 2020 Elsevier B.V. All rights reserved.