The SI-F method suggested by Iwasaki et. al, as the reasonable damage detection method This method detected the damage of the structure by using statistical analysis above the con-elation between the sensor outputs. In this method, con-elation between sensor output will be identified by using the response surface method and the similarity of the correlation is tested by using statistical Ftest. In the present paper, the results of experiment for the influence of the sensor position to the accuracy in fatigue damage monitoring of pipe using the SI-F method is shown to validate the optimization of the sensor position.