A clamping device includes a supporting bracket, a lifting assembly, a first adjusting assembly and a holding assembly. The supporting bracket includes a supporting member. The lifting assembly includes a first lifting member, a second lifting member, a fixed pulley, a connecting member and a clump weight. The first lifting member and the second lifting member are both slidably sleeved on the supporting member. The fixed pulley is mounted on the supporting member. The connecting member is arranged on the fixed pulley and couples the first lifting member to the second lifting member. The clump weight is detachably fixed to the first lifting member. The first adjusting assembly includes a first fixed member rotatably sleeved on the second lifting member and a first adjusting member rotatably sleeved to the first fixed member. The holding assembly is rotationally mounted on the first adjusting member.