The invention relates to a water pressure testing device of an intermediate heat exchanger. The invention adopts the technical scheme that the water pressure testing device of an intermediate heat exchanger comprises an upper flange arranged on a lower flange, wherein the upper flange and the lower flange are fixedly connected into a whole through a double-head bolt, a first nut and a first spacer; an inner flange is arranged in an inner hole of the upper flange, an upper press ring is arranged on the inner flange, and the upper press ring and the inner flange are fixedly connected into a whole through a mounting bolt, a second nut and a second spacer; the outer edge on the lower surface of the upper press ring is in lap joint with the upper flange; and a washer is also arranged between the upper press ring and the inner flange. A gap between the inner flange and the upper flange is much smaller than that before, and force acted on the upper press ring is much smaller than that of an original water pressure testing device, thus the invention has the advantages of sealing material saving and easy realization of sealing.