The invention relates to the technical field of soil erosion and forest hydrology, and discloses a slope water balance field observation device. The slope water balance field observation device comprises an isolation side wall, a header tank, a retaining wall and a collecting device, wherein the isolation side wall is arranged on the bed rock face of a slope, the header tank is arranged corresponding to the isolation side wall, a surface layer flow guide pipe and in-soil flow guide pipes are arranged in the retaining wall, the surface layer flow guide pipe is arranged corresponding to the header tank, and the surface layer flow guide pipe and the in-soil flow guide pipes are communicated with the collecting device. As the surface layer flow guide pipe and the in-soil flow guide pipes are arranged in the retaining wall, the slope water balance field observation device can observe interflow of soil in layers and verify a water balance equation well to comprehensively observe the slope water process; the slope water balance field observation device has the advantages of being simple in structure, facilitating observation and the like.