Variations of pressure along the vertical direction in a cylindrical silo are measured, of which the side wall is comprised of two separated up and down parts. The deviation of the measured results from the so-called Janssen model of silo stress is discussed. The measurements show that certain deviations from the model are always observed, no matter whether the slowly downward motion of silo bottom by “fully mobilized friction” as suggested by Vanel et al is carried on. Moreover without mobilizing the friction, the deviation may increase considerably if a tiny sink of the upper side-wall caused by weight of filled grains is present. The effect can be however eliminated by the friction mobilized. These indicate that distributions of grain weight at the bottom and lateral wall are complex and variant, and dependent on preparation manner and deformation of experiment setup. So stress boundary conditions need to be taken into account in the nonlinear elastic theory for analyzing static stress distribution of granular matter.