The output pressure is one of the most important feature of detonators. Using photonic doppler velocimetry （PDV） and impedance matching technique， a reliable measurement method for output pressure was carried out. The interface particle velocities between slapper detonators and optic windows were measured by PDV for three kind of detonators. The calculation results show the output pressures are 7.64， 7.29， 6.71 GPa， respectively. The PBX-RDX content has certain influence on the output pressure. As the PBX-RDX content decreases， the output pressure decreases. The output pressure of the three detonators were simulated by Ansys/Ls-Dyna. The simulated output pressures are 7.7， 7.1， 6.4 GPa， respectively. Comparing to the simulation， the pressure difference is less than 6.5%， which validates the method effective. The shell material has significant influence to detonator output pressure. For higher shock impedance， the output pressure is lower. Especially， the peak pressure for steel shell case is undistinguishable.