This invention belongs to the field of concrete material durability testing technology, specifically relates to a device for an annular tester of concrete gas permeability coefficient and its testing method. The device consists of a cover plate, a shell, a flowmeter, a sealing ring, and a test sample. The cover plate is located at the top of the shell, and the test sample is positioned inside the shell. Its outer wall is cylindrical, hollow in the interior, with a circular cross-section in the horizontal plane and a U-shaped longitudinal section. Both the top and bottom of the test sample are equipped with sealing gaskets. An air inlet on one side of the shell is connected to a compressed gas tank, and a central connecting channel is set up on the cover plate. The internal hollow part of the test sample is connected to the flowmeter through this connecting channel. During testing, place the test sample inside the shell, open the valve of the compressed gas tank, test the breathability of the test sample, maintain a balance time of 10 minutes to 20 minutes for each set of test samples, repeat the test 3 to 5 times with different test pressures, and repeat the testing process. The test involves measuring the gas flow through a sample to determine the average permeability coefficient of the sample. The average value of the permeability coefficients from 3 to 5 samples is taken as the test value for that group of samples. This invention has high accuracy, good repeatability of experiments, effective sealing, reliable test results, simple operation, and compact equipment that is easy to carry.