The invention discloses a span-adjustable bending test clamp with a positioning function, and belongs to the technical field of aircraft structure bending tests. The clamp comprises two clamp upper fulcrums, two clamp lower fulcrums, an upper clamp guide rail platform, a lower clamp guide rail platform and an acting barrel. The upper clamp guide rail platform and the lower clamp guide rail platform are provided with sliding rails respectively and provided with scales in the direction of the sliding rails. Threaded holes are formed in the sliding rails. The clamp upper fulcrums and the upper clamp guide rail platform are in sliding connection and are fixed through bolts. The clamp lower fulcrums and the lower clamp guide rail platform are in sliding connection and are fixed through bolts. The lower clamp guide rail platform is fixed to a test machine loading frame through a test machine lower chuck. The upper clamp guide rail platform is fixedly connected with the acting barrel through a test machine upper chuck. The problems that when large-load and large-deformation bend tests are carried out, the span of clamp fulcrums cannot be adjusted, and a clamp cannot adapt to test piece size changes or meet design requirements are solved.