Shock waves represent a primary form of damage from explosions， and explosive-driven shock tubes can simulate high overpressure shock wave scenarios. It is essential to determine test parameters， including the separation among the shock wave， explosion products， wave-front shape. Traditional pressure measurements， grounded in electrical principles， are insufficient for current flow field characterization research. Leveraging the reflection schlieren principle， a diagnostic system is developed for the shock tube nozzle's flow field. This system utilizes a laser source and sequence of optical elements. By integrating visual observations of flow phenomena with conventional pressure data， the method for analyzing flow field characteristics is enhanced. The findings indicate that the schlieren system captures high-resolution images of the shock wave and product flow field at the exit of the shock tube. Synchronized schlieren images， aligned with the pressure tests of the shock tube and ignition timings， offer insights into data oscillation， pressure anomalies， and the drift observed in piezoelectric pressure sensors. They also highlight the vibration effects in the nozzle and surrounding air， resulting from stress waves post-explosion within the tube. Through image analysis， the spatial decay patterns of the velocity and pressure of the shock wave at the explosive outlet of the shock tube can be obtained. These results furnish a novel diagnostic technique and analytical foundation， enhancing our comprehension of the formation and evolution of shock wave pressure in the explosive-driven shock tube.