Geometry of port-combustion chamber has an important effect on the performance of gasoline engines. Methods and approaches in reverse engineering are introduced into surface reconstruction and modification of a port-combustion chamber structure. Free-form surfaces of the port-combustion chamber structure for a gasoline engine with 4-valves and dual-ball type combustion chamber are successfully reconstructed in the reverse way through data processing, surface modeling, surface verifying, surface re-modeling and smooth evaluating etc., based on laser-scanned point cloud data of a sample work piece. It lays a foundation for imitation innovation of gasoline engine by changing the local structural characteristics and dimensions of a prototype model.