The utility model discloses an adjustable sample clamp for testing the transmittance of an optical material, belonging to the technical field of optical element testing and mainly solving the problems that a conventional sample cell for testing equipment has strict requirements on the verticality of test samples and requires that the samples have high machining accuracy. The adjustable sample clamp is mainly characterized by comprising a bottom plate, vertical brackets, spring steel sheets and movable brackets, wherein the vertical brackets are provided with test holes and are fixedly arranged on the bottom plate; the bottom plate is provided with grooves which are matched with the movable brackets and is locked and positioned through screws; one ends of the spring steel sheets are fixedly arranged on the movable brackets, and the other ends of the spring steel sheets extend to the test holes of the vertical brackets and are provided with light transmitting holes which are matched with the test holes; and the bottom plate is provided with two positioning holes which are connected with a spectrophotometer. The adjustable sample clamp has the characteristics of simple structure, easiness in adjustment, no requirements on the verticality of the samples and capability of realizing accurate testing of the transmittance of optical materials of different thicknesses, and is mainly used for testing the spectrum transmittance of the optical material.