The invention discloses a full-automatic permeation coefficient detection instrument and method for water permeable bricks. The detection instrument comprises an instrument casing, a high-position water storage tank, permeable sample sealing and fixing devices, overflow water tanks, a water storage pool, a full-automatic console and a sensing and control assembly, wherein an overflow cylinder in each permeable sample sealing and fixing device adopts a square column shape, an upper baffle is arranged at the lower part of the inner side of the overflow cylinder, a round hole I is formed in the center of the upper baffle, a seal ring is arranged on the lower surface of the upper baffle and on the periphery of the round hole I, a connection buckle is arranged between the outer side of the overflow cylinder and a lower end cover, a round hole II corresponding to the round hole I is formed in the center of the lower end cover, a seal ring is arranged on the upper surface of the lower end cover and on the periphery of the round hole II, a groove is formed in the closed position of the lower end cover and the overflow cylinder; and a seal pad is arranged in the groove. A detection part is connected with the full-automatic console, and a PLC (programmable logic controller) module system is arranged in the full-automatic console, so that the permeation coefficient of the water permeable brick can be detected automatically, the detection accuracy is high, errors of manual operation are reduced, the structure is simple, and the use is convenient.