The utility model relates to a gas-diffusion-free oil return device for hydraulic natural gas vehicle gas filling. The oil return device is characterized in that a first pneumatic valve, a second pneumatic valve, a third pneumatic valve and a fourth pneumatic valve constitute a bridge-type loop, a first port A of the bridge-type loop is communicated with a high pressure oil pump in a sealed manner, a second port B of the bridge-type loop is communicated with an inlet of a first detection bottle in a sealed manner, a third port C of the bridge-type loop is communicated with an oil basin in a sealed manner, and a fourth port D of the bridge-type loop is communicated with an inlet of a second detection bottle in a sealed manner; an outlet of the first detection bottle is communicated with an oil inlet of a first gas cylinder in a sealed manner through a fifth pneumatic valve, and a sixth pneumatic valve is fixed at a gas outlet of the first gas cylinder; and an outlet of the second detection bottle is communicated with an oil inlet of a second gas cylinder in a sealed manner through a seventh pneumatic valve, and an eighth pneumatic valve is fixed at a gas outlet of the second gas cylinder. The gas-diffusion-free oil return device is simple in structure and convenient to use, and natural gas is not wasted.