As a preview study, present research analysed the performance characteristics of a velocity compound supersonic impulse turbine with the rotor overlaps before adapting the overlap has the best turbine performance. This research was conducted for the turbine with square cross-section nozzles instead of axisymmetric nozzles and wrap around nozzles. Through 3-dimensional flow analysis for the turbine by a commercial flow analysis package, tip overlap case was more effective to improve the turbine performance than case hub overlap, and overlap case applied the hub and tip of the rotor had the largest improvement for the turbine performance in the cases. In case of overlap for the 2nd stage rotor, improvement of the turbine performance was not visibly large. Because, generated power in the 2nd stage is 22~23% of whole generated turbine power.