In order to investigate and reveal the influence of granularity on mechanical behavior in the short and long term load, the conventional and creep test are conducted on coarse sand stone, medium sandstone and fine sandstone of a project. Research shows that: the strength and deformation capacity increase with the decrease of granularity under the same confining pressure; the strength, deformation and elastic modulus increase linearly with the confining pressure increasing under the same size; The steady creep rate decreases with the grain of sandstone size under the same size and confining pressure ; Steady creep rate with partial stress increased exponential function growth under the same deviator stress and confining stress; Steady creep rate is smaller with the confining pressure increasing under the same size and partial stress; Three kinds of particle size of sandstone under long-term load corresponding strength than short-term value decreased by 40~60%;The internal friction angle and cohesion are compared with the short-term value reduced by 40% and 40~50%.