The invention discloses a device for testing the mechanical properties of a thin sheet under simple shear loading. The device comprises a base, a left clamp assembly and a right clamp assembly oppositely arranged along the length direction of the base in parallel, a slider, and a fixing block of a concave structure, wherein the right clamp assembly is fixed on the slider; the slider is embedded in the fixing block; the fixing block is fixed on the base; the slider can slide on the fixing block to enable the right clamp assembly to move close to or away from the left clamp assembly; a draw barfor adjusting the distance between the left clamp assembly and the right clamp assembly is arranged between the fixing block and the slider; the left clamp assembly is fixed on a core; the core is fixed on the base through a second rail assembly; and the core can slide freely along the length direction of the base through the second rail assembly. Through the reasonable structure design, the device can achieve the more stable measurement in the thin sheet simple shearing test, and can flexibly adjust the distance between chucks clamping the sheet, thereby obtaining more accurate test data, and providing a method for studying the mechanical properties of the thin sheet under complex loading state.