The disclosure discloses a testing device and a testing system for testing high-pressure and large-scale gap dynamic sealing performance of a plunger sleeve. The testing device includes two cylinders, first and second plunger rods and a piston rod. A first chamber is formed between an end of the first plunger rod and a first cylinder, and a second chamber is formed between an end of the second plunger rod and a second cylinder. The first chamber and the second chamber are provided with high-pressure liquid, and the two chambers communicate with each other. When being driven by a driving device, the piston rod drives the first and second plunger rods to reciprocate left and right. The plunger sleeve and a locking plunger sleeve are disposed outside each of the first and second plunger rods. The locking plunger sleeve has a leakage port. When the first and second plunger rods reciprocate, the high-pressure liquid in the chambers leaks from the leakage port.