The invention relates to the technical field of measurement of content of radioactive substances and provides a measuring device for tritium content of tritium gas. The measuring device is used for solving the problems in the prior art that the measurement of the tritium content of the tritium gas is greatly affected by environments and the accuracy of measurement is low. The measuring device comprises a temperature control structure with a cavity, a first thermostat and a second thermostat, wherein the first thermostat and the second thermostat are separately arranged in the cavity and are of hollow structures. A sample chamber which is used for accommodating the tritium gas is arranged in the first thermostat. A control chamber which is used for accommodating a control is arranged in the second thermostat. The measuring device is further provided with a measuring circuit and a checking heat source, wherein the measuring circuit comprises a pyroelectric unit made up of a plurality of heat sensitive elements which are separately arranged on the sample chamber and the control chamber and are electrically connected with one another. The invention further provides a measuring method for the tritium content of the tritium gas based on the measuring device. The device and the method have the beneficial effects that the environmental influence is little, the accuracy of measurement is high, and industrial requirements are met.