As the open idea becomes popular in modern interior design, some function places are gradually transformed into open or half-open places, and the cognition of these types of places becomes a new challenge to service robots. An algorithm based on the prototype theory of cognitive psychology is proposed to improve the robots’ ability of open interior-places cognition. Firstly, the prototype model of place concept is designed, and it mainly includes a description about feature objects belonging to a place concept and a description about typical spatial relation among these objects. Secondly, a similarity measure function and a scoring criterion for spatial relation are proposed, and they are used to measure similarity between current environment and prototypes of place concepts. Finally, the perception toward place region is considered, and the influence on place-concepts perception is also discussed which is caused by overlap of place regions. The algorithm is verified through simulation, and the results suggest that the open interior-places perception can be achieved by the proposed algorithm. Moreover, it is flexible and robust to some extent.