The invention relates to a novel micro-flow gas mass flow controller, which comprises an inlet cover, a sealing ring 1, a fastening piece, a spring, a valve core, a sleeve, a steel ball, sealing rings 2, an ejector rod and a locking nut, and is characterized in that a circular throttling seam is formed through a radial clearance of 4[mu]m-10[mu]m between the sleeve and the valve core, micro-flow control is realized through the circular throttling seam after a gaseous working medium gets into the controller through the gas inlet, and accurate output of micro flow of 20[mu]g/s-2mg/s under specific pressure is realized. According to the invention, the valve core and a valve sleeve are in hole-shaft fit, throttling control is realized through the circular seam, the processing technology is simple, the reliability is high, and the anti-pollution ability is high. The position of the valve core is adjusted by using an adjusting device, the adjustment range is large, and flow output of the controller under the specific pressure can be accurately adjusted. Through adjusting the inlet pressure, the flow output range changes greatly, the flow control range can reach up to more than 100 times, and the novel micro-flow gas mass flow controller can be applicable to multi-mode working conditions of a system and occasions in which the flow of a working medium is required to be continuously changeable.