The multi-hole orifice plate is a simple hydrodynamic device which can be used for intensification of liquid-liquid heterogeneous micromixing for preparing biodiesel or emulsified diesel. A flow visualization experiment system with transparent hydrodynamic cavitation reactor was set up to investigate the cavitation in the orifice plate and the outlet of the orifice plate. The effects of upstream pressure and cavitation number on the change of hydrodynamic cavitation were investigated. As the cavitation in orifice plates is transient, the numerical simulation was combined to give a more detailed flow insight and predict the cavitation inception and development. SST and LES models were used to simulate the cavitating flow in orifice plates. The experimental results showed that with the increase of upstream pressure the cavitation incepted in the orifice plate, and the discharge coefficient increased at first. In the next stage, cavitation extended to the outlet of the testing orifice plate with the decrease of discharge coefficient which was caused by cavitation choking flow. Also from the experimental images, it was concluded that some cavity bubbles merged into large-scale bubbles and existed in the downstream region of the orifice plate which seemed to cause the choking flow. Compared the numerical simulation results with the experimental results measured by high speed camera, it was found that SST model can predict the average length of cavitation but it can hardly simulate the transient cavitating flow. LES model can well predict the cloud cavitation and the re-entrant jet which is central to the process of cloud cavitation shedding. The results also showed that with the development and collapse of cloud cavitation, the length of cavity changed periodically. In addition, the detatils of the re-entrant jet were shown in LES simulation.