The invention relates to a ring shear test instrument suitable for a vertical shear surface. The ring shear test instrument comprises a shear box, a lifting system, a power rotating system, a monitoring and controlling system and a frame. In the shear box, shear plates are evenly fixed to an annular bottom plate in the radial direction of the annular bottom plate, and a shear box outer cover is buckled to the annular bottom plate and the shear plates in a covering mode and is assembled and fixed to the annular bottom plate through guide bars and guide grooves; the shear box outer cover is connected with a rotating force arm of the power rotating system to transmit torque, a coupling shaft pressing plate is embedded in a center hole of a top plate of the shear box outer cover in a centered mode and is driven by the lifting system to conduct normal force loading, the annular bottom plate is embedded in a cylindrical supporting platform in a centered mode, and an inner cylindrical side face generated when the annular bottom plate drives the shear plates to conduct circular motion under the action of rotating torque is a vertical shear surface. The ring shear test instrument can ensure that shear displacement and shear stress on the shear surface are uniformly distributed, the thickness of the vertical shear surface is not limited, and thus a large ring shear test in the presence of large particulate matter is realized.