The invention belongs to the technical field of petroleum drilling, and particularly discloses a drilling fluid invasion depth testing device which comprises a support, a glass core barrel, a drillingfluid container, a heating device for heating drilling fluid and a medium delivery device. The glass core barrel is horizontally arranged to the support, the inside of the glass core barrel is filledwith quartz sand with a preset length section, measure scales are arranged on the outer wall of the glass core barrel along the length direction, and a sealing end cover is arranged at each of two ends of the glass core barrel; one end of the medium delivery device is connected to one end of the glass core barrel while the other end of the same is connected to the drilling fluid container. The invention further discloses a testing method applying the drilling fluid invasion depth testing device. By the drilling fluid invasion depth testing device and the testing method, depth and state when drilling fluid invades a reservoir can be visually and quantitatively simulated and tested, and a basis is provided for evaluating degree of damage caused to the oil-gas reservoir by the drilling fluidand selecting the drilling fluid good for the oil-gas reservoir.