Parking issues have been one of the significant transport problems in central metropolitan areas due to intensive land use and lacking parking spaces. This study presents an approach to evaluating and optimizing a new Tradable Parking Permit scheme for Sharing Parking (TPPSP) in nonpublic parking areas (NPAs). Special emphasis is put on improving the utilization of parking places under multimodal transport systems and equity among different users, which has been overlooked in previous relevant studies. The nested-logit-based user equilibrium condition under multimodal transport systems for the TPPSP scheme is modeled and solved by a variational inequality model, incorporating a quantal response equilibrium dedicated to depicting non-cooperative cruise-for-parking competition. Especially, the model takes into account the heterogeneous users’ choice behavior regarding travel modes and routes. The proposed model not only investigates the impacts of the TPPSP scheme on the performance of the road networks and parking facilities but also the equity of various users. Afterward, a mathematical program with equilibrium constraints is utilized to optimize equity measured by the Gini coefficient and solved by the Kriging metamodel algorithm. Numerical experiments are utilized to validate the proposed approaches. The results show that the proposed TPPSP scheme is an effective approach to promoting social welfare by improving the performance of road networks and parking facilities outside the NPAs and balancing the equity of different users simultaneously. The outcomes provide a potential and useful pricing and management strategy for improving parking issues in urban contexts.