The Indoor relative permeability curve test often adopts unsteady state method. The traditional measurement method does not consider the end effect and the calculation error of the relative permeability curve. Based on the study of the end effect mechanism, a mathematical model considering the end effect of tight sandstone is established. The error of the end effect and the JBN calculation method for the relative permeability curve test of the tight sandstone core in the unsteady state is analyzed. The research shows that increasing the displacement pressure difference or increasing the core length can effectively reduce the test error caused by the end effect, but there is a limit value for the reduction. At the same time, only changing the experimental conditions can not completely eliminate the test error caused by the JBN calculation method. Therefore, there is a calibration plate for determining the phase permeability curve of a tight sandstone core with unsteady state considering the end effect. It can ensure the accuracy of the relative permeability curve test results and improve the credibility of the oilfield production dynamic prediction.