With the annual increase of urban motor vehicle ownership, the road network in the old city has been unable to meet the increasing traffic demand, resulting in congestion. Malformed intersection has become one of the main factors causing congestion in the road network of old city because of its strange linear shape, many conflict points and low service level. Therefore, it is of great significance to excavate the traffic potential of all kinds of malformed intersections and explore the reconstruction and design methods for alleviating urban traffic congestion and improving the service level of road network. This paper expounds the classification, existing problems and improvement methods of malformed intersection, and takes the intersection of Renmin Road and Fengjing Road unfavourably in Xi "an City as an example to conduct practical test and obtain good results, which has reference value for the reconstruction of various malformed intersection in the future.