Aiming at the problem that the lever-arm velocity error between the measured speeds of one-dimensional Laser Doppler Velocimeter (1D-LDV) and Strapdown Inertial Navigation System (SINS) caused by their different installation positions in the vehicle-mounted integrated navigation systems composed of 1D-LDV and SINS, an online calibration algorithm based on Kalman filter is proposed to calibrate and compensate the mounting lever-arm. By introducing a reference point that maintains alignment between the velocity direction and the carrier's direction of motion during movement, the traditional lever-arm velocity error model was improved, so that it can accurately characterize the actual relationship between the measured velocities from the 1D-LDV and SINS. The vehicle experiment results show that the calibration algorithm can effectively calibrate the arm error between 1D-LDV and SINS. By using the 1D-LDV measured velocity (after lever-arm error compensation) and the gyroscopic data from the SINS to perform dead reckoning, the horizontal positioning errors in two experimental trials are reduced from 8.80 m and 6.60 m to 7.07 m and 5.48 m respectively, demonstrating a moderate improvement in navigation and positioning accuracy.