Abstract: A multi-posture stride length calibration system for indoor positioning includes: at least an inertial measurement unit, configured to sense at least a signal; a signal preprocessing unit, connected to the inertial measurement unit to process sensed signal; a multi-posture determination unit, configured to determine at least a posture based on processed signal; a step-computing decision unit, configured to compute a number of steps and a step frequency based on processed signal; a map feature calibration unit, configured to receive the number of steps, step frequency and posture to determined a stride length and decide whether the stride length matching a criterion; a step-computing threshold adjustment unit, configured to adjust a step-computing threshold if stride length not matching the criterion; and a stride length regression unit, configured to update a stride length regression curve for posture based on step frequency and stride length if stride length matching the criterion.