Numerical and experimental studies of cross sectional optical power distribution (OPD) in polymer optical fiber under offset launch are given. The OPD of fibers with various lengths and under various launch offsets are numerically simulated by using ray tracing method and measured by two-dimensional CMOS image detector array. Results show that the OPD shifts gradually away from axis center and forms ring with increasing of launch offset and the circular uniformity increases with the length of fiber. OPD measurements are taken on bend fibers under center launch. It is indicated that the OPD shift gradually away from axis to outer radii with the decrease of curvature radii when curvature radii are far greater than critical radius of curvature. When curvature radii decrease to critical radius, the OPD is significantly broaden under mode coupling effect.