The invention discloses a pressure control device and a gas diffusion coefficient measuring device thereof. The pressure control comprises a first container with a first opening, a second opening and a third opening, a second container with a fourth opening, a fifth opening and a sixth opening, a liquid supply unit and an equalizing pipeline, wherein the first opening is used for being connected with the first end of a core holder; the fourth opening is used for being connected with the second end of the core holder; two ends of the equalizing pipeline are respectively communicated with the first container and the second container, the equalizing pipeline comprises a horizontal pipeline section, a sliding piece for sealing dividing of the inner part of the horizontal pipeline section is arranged in the horizontal pipeline section, and can horizontally slide in the horizontal pipeline section to equalize pressure on the two sides of the sliding piece. According to the pressure control device and the gas diffusion coefficient measuring device, the gas pressure at the two ends of a tested core in the gaseous diffusion coefficient measuring process can be kept consistent.