Barriers which can reduce the energy of debris flows are frequently constructed as a mitigation measure against debris flow damages. However, the effect of barriers on characteristics of the debris flow is not fully understood. This research investigated the interactions between the debris flow and barriers and analyzed the effect of barrier location along a channel using the smoothed particle hydrodynamics (SPH) method. We chose a site in Yeoju, Korea, as the model site, where a debris flow event occurred. Volume and soil properties were acquired from the site investigation and calibration of the rheological properties were conducted with reference to the deposit area of the debris flow shown in Google Earth. In the site, the closed-type barrier was installed at different four locations from upstream to downstream of a flow channel, respectively; and the reference debris flows were then simulated while observing velocity and volume of the debris flows. By installing the barrier, the velocity and volume of the debris flow were observed to decrease significantly, compared to the case with no barrier. In particular, installation of the barrier at downstream of the channel resulted in the greatest reduction in the kinematic energy. These results are different from general event, which has only one source at the top of the channel. It is impossible to prevent the debris flows generated at downstream of the barrier because there are five sources at different locations. In conclusion, it is advantageous to install the barrier in the downstream part where debris flows are combined in case of multiple sources. The obtained results give contributions to better understanding of the debris flow behaviors considering the barriers as a mitigation measure, and can be used for an optimum and efficient design of the debris flow barriers on practical work.