In order to solve the problems when designing super-light structure part such as needing complex design techniques, long design cycle, difficult to add skin if making it by additive manufacturing technology, based on selective laser melting technology, a method which can automatically add skinned super-light structure to traditional metal part CAD model was put forward in this paper. Considering the selective laser melting process characteristics, through an algorithm, a skinned super-light quasi-honeycomb structure part model with a preset porosity can be automatically designed by transforming an original CAD model. And the new part model data format can direct drive a selective laser melting machine for additive manufacturing without any data format transformation. The construction and design method of the skinned super-light structure of metal part were studied. Through process analysis, appropriate processing unit length and reasonable skin tissue of super-light structure metal part were gotten. The above method was tested successfully on a part model with complex shape in a selective laser melting experiment. The error of porosity is 2.79%, which means that this method can accurately reduce part mass according to preset porosity value. Therefore, in this way, skinned super-light structure part can be design automatically and quickly based on an original CAD model without super-light structure, the burden to design this kind of parts will be greatly reduced, and the practicability of the parts made through this method will be improved greatly.