Aerodynamic performance of the simplified test model of clustered linear aerospike nozzles was experimentally investigated and results were compared with those of a theoretical model. The model is focused on predicting the ramp pressure distribution in the case of external-flow-exposed conditions. The test model has three or four clustered cell nozzles with a designed Mach number of 3.47 and is connected to a straight section and a 12- degree-inclined straight ramp. It is set up in a Mach 2.0 supersonic wind tunnel to simulate conditions of supersonic external flow impinging on the cell nozzle jets and ramp surface. Under conditions with or without external flow, pressure distributions on the ramp surface and cell base pressures were measured. Results of measured pressure distributions on the test model surface were obviously different due to the external flow: ramp surface pressures were maintained at a certain level above the environmental pressure level according to the cell flow conditions, and the pressure distribution for conditions without-external flow can be nearly approximated by the method of characteristics. This pressure behavior was successfully predicted by the theoretical model established in this study. Furthermore, the external flow makes the entire flowfield more two-dimensional compared to that for the conditions without-external flow. The influence of external flow on the cell base pressure behavior was found as reduced cell base pressure distribution due to virtually and locally accelerated external flow at the lip on the top wall of the cell nozzle exit.