The invention relates to the technical field of LNG tanks, and in particularly to a cold inspection test device and method for an insulating layer of an LNG marine tank, and the cold inspection test device for the insulating layer of the LNG marine tank comprises the following parts of a low temperature medium container used to storage a low temperature medium having a boiling point less than or equal to minus 163 DEG C; a first branch, of which the inlet end is communicated with the low temperature medium container, and the outlet end is communicated with the LNG tank, wherein the first branch is provided with a vaporizer and a first regulating valve, the vaporizer is used to vaporize a liquid low temperature medium into a gas low temperature medium, and the first regulating valve is communicated with the output end of the vaporize to control the transmission of the gas low temperature medium flowing in the first branch; and a second branch, of which the inlet end is communicated withthe low temperature medium container, and the outlet end is communicated with the LNG tank to transmit the liquid low temperature medium to the LNG tank, wherein the second branch is provided with asecond regulating valve used to control the transmission of the liquid low temperature medium flowing in the second branch. The cold inspection test device and method provided by the invention facilitate the technical personnel to effectively detect the insulating layer of the LNG tank.