An automatic measuring instrument for measuring a natural gas content contained in an unconventional natural gas reservoir sample, the automatic measuring instrument comprises: a sample receiving 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 and a computer, wherein the lower end of the gas collection measuring cylinder is open and the upper end thereof is sealed by a first sealing cover; a first floating sheet is arranged in the gas collection measuring cylinder; the lower end of the balance measuring cylinder is open and the upper end thereof is sealed by a second sealing cover; a second floating sheet is arranged in the gas collection measuring cylinder; both the lower ports of the gas collection measuring cylinder 3 and the balance measuring cylinder 4 are placed in the liquid storage tank and below the liquid level of the liquid storage tank; the sample receiving tank is placed in the thermostatic water bath box and consists of a tank body and a third sealing cover, wherein a temperature transmitter is arranged on the third sealing cover; a first photoelectric liquid level sensor is arranged on the first sealing cover; a second photoelectric liquid level sensor is arranged on the second sealing cover; a first gas guide tube is connected to the internal space of the sample receiving tank and the internal space of the gas collection measuring cylinder; a second gas guide tube is connected to the internal space of the balance measuring cylinder and external atmosphere; a first electromagnetic valve is arranged on the first gas guide tube; the first gas guide tube is also connected with an evacuation branch gas tube which is equipped with a second electromagnetic valve; the temperature transmitter, the first photoelectric liquid level sensor, the second photoelectric liquid level sensor, the first electromagnetic valve, the second electromagnetic valve and a driving device of a lifting device are electrically connected with the data acquisition and control system respectively; the data acquisition and control system is electrically connected with the upper computer; and the automatic measuring instrument further comprises a lifting device for driving the gas collection measuring cylinder and the balance measuring cylinder to move up and down relative to the liquid storage tank, wherein a protecting cap is also arranged at the lower end of said gas collection measuring cylinder and the lower end of said balance measuring cylinder respectively, and an axial through hole is formed in the middle of each protecting cap, wherein the hole diameter of each through hole is smaller than the outer diameter of the first floating sheet and the outer diameter of the second floating sheet. a sample receiving 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 and a computer, wherein the lower end of the gas collection measuring cylinder is open and the upper end thereof is sealed by a first sealing cover; a first floating sheet is arranged in the gas collection measuring cylinder; the lower end of the balance measuring cylinder is open and the upper end thereof is sealed by a second sealing cover; a second floating sheet is arranged in the gas collection measuring cylinder; both the lower ports of the gas collection measuring cylinder 3 and the balance measuring cylinder 4 are placed in the liquid storage tank and below the liquid level of the liquid storage tank; the sample receiving tank is placed in the thermostatic water bath box and consists of a tank body and a third sealing cover, wherein a temperature transmitter is arranged on the third sealing cover; a first photoelectric liquid level sensor is arranged on the first sealing cover; a second photoelectric liquid level sensor is arranged on the second sealing cover; a first gas guide tube is connected to the internal space of the sample receiving tank and the internal space of the gas collection measuring cylinder; a second gas guide tube is connected to the internal space of the balance measuring cylinder and external atmosphere; a first electromagnetic valve is arranged on the first gas guide tube; the first gas guide tube is also connected with an evacuation branch gas tube which is equipped with a second electromagnetic valve; the temperature transmitter, the first photoelectric liquid level sensor, the second photoelectric liquid level sensor, the first electromagnetic valve, the second electromagnetic valve and a driving device of a lifting device are electrically connected with the data acquisition and control system respectively; the data acquisition and control system is electrically connected with the upper computer; and the automatic measuring instrument further comprises a lifting device for driving the gas collection measuring cylinder and the balance measuring cylinder to move up and down relative to the liquid storage tank, wherein a protecting cap is also arranged at the lower end of said gas collection measuring cylinder and the lower end of said balance measuring cylinder respectively, and an axial through hole is formed in the middle of each protecting cap, wherein the hole diameter of each through hole is smaller than the outer diameter of the first floating sheet and the outer diameter of the second floating sheet.