It is necessary to test a newly built model to make sure that it does simulate the actual system. The test may include many aspects, such as sensitive test, comparison test with history data, etc. This paper studies sensitive test and presents some results of the findings.In studying the structure of a given system, the endogenous variables and exogenous variables are given explicitly. If we can not tell the difference between them correctly, it may confuse the real meaning of the sensitive test.In the present analysis we find that the conditions for non-sensitivity of variables to a model are: 1) the change is made for one variable only and 2) the change is small. The conditions for sensitivity of the variables to the model are: 1) two or more variables change at the same time and 2) the change is great. A model may also become sensitive for a small change of the exogenous variable.The above results have been thoroughly investigated and the methods of the sensitive test are presented.