In microscale deformation, the magnitudes of specimen and grain sizes are usually identical, and sizedependent phenomena of deformation behavior occur, namely, size effects. In this study, size effects in microcylindrical compression were investigated experimentally. It was found that, with the increase of grain size and decrease of specimen size, flow stress decreases and inhomogeneous material flow increases. These size effects tend to be more distinct with miniaturization. Thereafter, a modified model considering orientation distribution of surface grains and continuity between surface grains and inner grains is developed to model size effects in microforming. Through finite element simulation, the effects of specimen size, grain size, and orientation of surface grains on the flow stress and inhomogeneous deformation were analyzed. There is a good agreement between experimental and simulation results. In microscale deformation, the magnitudes of specimen and grain sizes are usually identical, and size dependent phenomena of deformation behavior occur, ie, size effects. In this study, size effects in microcylindrical compression were investigated experimentally. It was found that, with the increase of大 尺寸, of of specimen specimen specimen specimen specimen,, These These These These Thereafter Thereafter Thereafter Thereafter Thereafter Thereafter Thereafter Thereafter Thereafter Thereafter Thereafter Thereafter Thereafter Thereafter Thereafter grain grain grain grain grain grain grain grain grain grain grain grain grain model size effects in microforming. The effects of specimen size, grain size, and orientation of surface grains on the flow stress and inhomogeneous deformation were analyzed. There is a good agreement between experimental and simulation results.