Abstract: To investigate the characteristics of 3-D viscous flowoutside multi-tube Pulse Detonation Engine (PDE), the 3-D viscous space-timeConservation Element and Solution Element(CE/SE) method was deduced tosimulate the flow-flied inside and outside Pulse Detonation Engine withseven tubes. In the multi-tube model, one tube is in the midst and the othersix tubes are around it with a circle. One-dimensional model was used forthe flow inside PDE, and three -dimensional model was adopted for the flowoutside PDE to obtain the varieties of the flow outside the multi-tube PDE.The results indicate that there are vortexes, shocks and expansion wavesoutside the multi-tube PDE. In addition, the results might be referrible toresearch the characteristics of the flow-field outside multi-tube PulseDetonation Engine.