The invention belongs to the technical field of in-situ testing in geotechnical engineering and relates to a field test device for the interfacial pressure between a miniature steel pipe pile and cement mortar, and a method. The force bearing face of a soil pressure box makes contact with a cement mortar stone body through sandy soil and a circular encapsulation membrane, the force bearing face ofthe soil pressure box bears force uniformly, the full section is pressed, thus stress concentration is avoided, and the soil-rock pressure of the soil-facing face of the miniature steel pipe pile istested more accurately; the surface of a pile body of the miniature steel pipe pile is provided with a matched protecting steel lantern ring, the soil pressure box is mounted in the protecting steel lantern ring, a cavity between the soil pressure box and the protecting steel lantern ring is filled with epoxy resin, thus the soil pressure box is fully protected, and the survival rate of the soil pressure box is increased significantly; and an observation cable is guided out from the middle of the bottom face of the soil pressure box and guided to the pile top along the inner wall of the miniature steel pipe pile, field mounting is convenient, and the observation cable of the soil pressure box is not damaged in the process that the miniature steel pipe pile is sunken into a drilled hole.