AbstractOptical pulse measuring instruments (OTDRs) are very useful in locating broken areas and assessing the homogeneity of optical fibers, etc. Until now, the theoretical relation between the measured results of the optical and splicing losses of cut‐back and OTDR methods was not known and OTDRs were not used to measure losses of steady‐state mode distributions. This study investigates the backscattering mode distribution of graded‐index optical fibers using geometrical optics. The launching condition of the light pulse and the receiving condition of back‐scattering, and their relation to the measured optical and splicing losses, are determined. The theoretical and experimental relation between the measured values of backscattering by OTDR and cut‐back methods is also discussed. As a result, it is shown that the steady‐state condition of the received backscattering light is necessary when measuring the losses of steady‐state mode distribution by OTDR method. We propose the possibility of estimating the splicing loss values of the cut‐back method from the difference of the splicing loss measurements under varied launching conditions of OTDR method. Correctness of this method is confirmed experimentally. In this method, no previous preparation is required and by changing the launching conditions at only one end, only two measurements are made and a simple calculation is required. Therefore, it is expected that measurement efforts are significantly reduced by this method.