In order to investigate the flow behavior of pressure letdown in dense-phase pneumatic conveying at high pressure, experiments using pulverized coal were carried out at a conveying facility with pressures up to 3.0 MPa. The effects of the pressure letdown structure, operation parameter and particle size on the flow characteristics of the pressure letdown were studied. Empirical correlation of pressure drop through the pressure letdown was derived using the Barth additional theory and experimental results. The results show that the solid loading ratio and gas velocity have a stronger effect on the pressure drop through the pressure letdown. The flow characteristics of gas-solid two-phase flow across the different sections of the pressure letdown were characterized and examined. Pressure drops rise with increasing particle size or pipe diameter ratio at similar operating parameters. The empirical model of the pressure drop through the pressure letdown was derived and the predicted values agree well with experimental results, with relative deviations less than +/- 10%. The flow characteristics of the pressure letdown offer the theoretical support for design, control and operation of dense-phase pneumatic conveying at high pressure.