<p>The accuracy and reliability of vehicle navigation are facing severe challenges in urban environments. Due to the time-increasing INS (Inertial Navigation System) errors, traditional GNSS (Global Navigation Satellite System) and INS integrated navigation method cannot maintain high-precision positioning performance under poor GNSS observation conditions for a long time. In order to improve the accuracy of position and attitude estimation, an enhanced GNSS/INS positioning method with position and attitude constraints was proposed based on the traditional loosely coupled GNSS/INS integration. Position constraint information from light detection and ranging (LiDAR) and attitude constraint information from time-difference-carrier-phase and non-holonomic constraints were adopted to correct the integrated navigation errors. The simulation results showed that the positioning accuracy of the proposed method can reach centimeter level. Compared with the traditional GNSS/INS integration, the positioning accuracy was improved by 76%, 68% and 65% respectively in three simulated signal blockage environments. In addition, the corresponding attitude accuracy was improved as well, with the most notable improvement in yaw accuracy, which increased by about 75%, 74% and 76%, respectively. In the real GNSS signal blockage experiment, the proposed algorithm was also superior to the traditional one<b>,</b> with accuracy improvements of about 93% in position and 36% in attitude.</p>