A novel ground measuring device to measure natural gas output at producing layer returned from an under-balanced drilling shaft comprises a flange, a main connecting pipe, a butterfly valve, a throttle valve pipe, an orifice throttling set, a measuring transducer interface, a bypass connecting pipe and a bypass siphon. Wherein, the flange is connected with a ground vent pipe manifold flange. The main connecting pipe is connected with the throttle valve pipe through a bolt. A middle flange is connected with the butterfly valve. In addition, the orifice throttling set is connected with the throttle valve pipe through a flange. An upper end and a lower end of the orifice throttling device are provided with a measuring transducer interface. A measuring transducer is inserted into an interface 6. Besides, the butterfly valve is connected with the main connecting pipe and the bypass connecting pipe through welding. The bypass connecting pipe is welded with the bypass siphon. The utility model removes the defect that no measuring device to measure the gas overflowed onto ground from the oil-gas producing layer in the under-balanced drilling shaft and is widely suitable for measuring natural gas output from the under-balanced drilling shaft.