Abstract: A photovoltaic module mounting system having a rack structure, which includes a mounting rack structure having a rail (5) and two clamps (6) for holding a photovoltaic module (7) by a bolt (3) extending from a press plate (4) on an outer side of the module (7) to one of the clamps (6) mounted in an upper input space (51A) in the rail (5). Entrances (50A and 50B) are provided relatively for each of the two input spaces (51A and 51B) each providing a space to input one of the at least two clamps (6), which are mutual perpendicular. The longitudinal input space (51A) in the upper section of the substantially H shape rail is used to hold the clamp (6) to fix the photovoltaic module (7). The lateral input space (51B) is used to hold the clamp (6) to fix the rail (5) to the pre-location. It has an excellent function on lateral and longitudinal location. And the structure is simple, compact, efficient, adaptable and saves on material.