Hollow plastic parts can be made by a large number of manufacturing method, but rotational molding offers the ability to create one-piece, stress-free parts with attractive economics and is specially suited for making article with complicated geometrics and excellent detail reproduction. In this process the product is formed inside a closed mold or cavity, while the mold is rotated biaxially. The fundamental nature of rotational molding is such that low-pressure process, relatively high temperature and long cycle time. however, a drawback of this process has always been the surface pin-holes which occure in the products due to air trapping between mold surface and polymer in sintering step and donَ t exist requirement driving force for removal of air bubble.in this study by effect of PEG400 and its investigation, pin- hole problem is solved without any main impact to mechanical properties.0.5% PEG400 by affecting on surface tension of polymer powder, thermal capacity, contact angle and as modifier of powder structure could solved the pin-holes problem completely.