An automatic measuring instrument for an unconventional natural gas content includes a parsing tank, a thermostatic water bath box, a gas collection measuring cylinder, a balance measuring cylinder, a liquid storage tank, a data acquisition and control system, an upper computer, and a lifting device for driving the gas collection measuring cylinder and the balance measuring cylinder to move relative to the liquid storage tank, wherein both the lower ports of the gas collection measuring cylinder and the balance measuring cylinder are placed below the liquid level of the liquid storage tank. The parsing tank is placed in the thermostatic water bath box. A gas guide tube A is connected to the parsing tank and the gas collection measuring cylinder. A gas guide tube B is connected to the balance measuring cylinder and the outside atmosphere is fed therein. By the adoption of the measuring instrument, the constant-pressure isasteric automatic continuous measurement of the content of natural gas contained in an unconventional natural gas reservoir sample is achieved. Moreover, the measuring instrument is simple in structure, reliable in measurement and analysis results, convenient in operation and high in measurement accuracy.