The present invention relates to an HXN5B locomotive fuel injector testbed clamp. The HXN5B locomotive fuel injector testbed clamp comprises a testbed, a compound hydraulic cylinder, a first movable clamp block, a second movable clamp block, guide posts and a fixed pressing block. The compound hydraulic cylinder is installed on the panel of the testbed, a piston rod of the compound hydraulic cylinder comprises an outer piston rod and an inner piston rod, one ends of the guide posts are fixed on the panel, the fixed pressing block is fixed at the other ends of the guide posts, the first movableclamp block and the second clamp block are arranged between the two guide posts, the inner piton rod is internally provided with an oil supply hole channel, a high-pressure fuel pipeline is accessedinto the oil supply hole channel of the inner piston rod, high-pressure fuel is extended out of a high-pressure interface of a compressing seal fuel injector and then enters the fuel injector throughthe inner piston rod; and the outer piston rod is extended through the first movable clamp block, the second movable clamp block, the guide posts, the fixed pressing block and the compressing seal fuel injector so as to achieve rapid clamping of the HXN5B locomotive fuel injector. The HXN5B locomotive fuel injector testbed clamp achieve fast clamping of the fuel injector, saves time and labor, isconvenient and rapid in operation and safe and reliable.