We choose a plug cluster nozzle targeting use with geostationary satellites, from the perspective of installation restrictions on rockets and performance improvement. The flow properties were determined via tests and analysis using a feasibility sample scale model plug cluster nozzle, the expansion area ratio e of which was 150. We selected a plug cluster nozzle with the restriction condition and performance improvement in mind (a fusion-type plug cluster engine and cluster engine). The lack of any notable shock wave sailing across the nozzle exit plane, which would tend to cause slowdown of the exhaust gases, as seen in the module overlap region during the feasibility sample scale model test, gave us reason to believe the performance may improve when the plug cluster nozzle is used. In addition, its use was also expected to boost the base part pressure performance. No major interference between the module exhaust gases suggested no problematic heat load was likely to affect the nozzle when the combustion gases were used. Subsequently, we investigated the effect of the module overlap ratio on performance by a parameter survey on a low expansion area ratio (e25) scale model test. These nozzles showed relatively low performance due to the shock waves caused by the low expansion ratio. We attempted to estimate simply the thrust of the 8-module plug cluster nozzle using 2- or 3module cluster nozzles to reduce the cost of the study, but the estimated figures did not correlate with the thrust loss even of the low overlap ratio nozzles. We consider this attributable to the different gain zone areas, the location of the loss zone and the base pressure effect etc. This investigation will be continued by analysis and testing. Subsequently, we plan to engage in testing using the parameter survey higher expansion area ratio (e>50) scale model because the low expansion ratio nozzles have less performance by strong shock waves upstream of the nozzle exit.