Abstract: This paper analyzes the great effect of injection transfer characteristics on limit point operation parameters in an injector and flow character of injected flow according to injector limit point data measured in tests of Science Foundation Subject No.24001.The actual flow mode at injector limit point is presented.The paper also analyzes the impassability of limit expansion ratio for the injector and the reason why the limit expansion ratio calculated from the injector engineering method is much less than its value obtained from the tests.The eyisting conclusion that “the injector limit expansion ratio is the highest possible pressure ratio” is refuted by the theoretical demonstration and injector operation characteristics measured in tests.It is proved that the operational expansion ratio can be increased much beyond the limit expasion ratio when the injector absorbs injection transfer mass.The “Operation test characteristics of injector” from low expansion ratio to high expanion ratio beyond the limit expansion ratio is first accomplished.