The invention belongs to the technical field of fuel injecting systems of internal combustion machines, and in particular, relates to a gas fuel injector. The gas fuel injector comprises a valve body,an oil tank, a gas rail and a hydraulic common rail; a gas hole in the valve body communicates with the gas rail; a needle valve control cavity is formed between a needle valve in the valve body andan intermediate body; and the needle valve control cavity communicates with the hydraulic common rail through an oil inlet hole in the intermediate body, and communicates with the oil tank through a communicating valve. The gas fuel injector has the following beneficial effects: the injector is applied to a compressed natural gas direct injecting technology, and is high in engine compression ratioand heat efficiency, low in fuel consumption and capable of meeting higher and higher emission standard requirements; the injector controls the injecting time and the injecting quantity of natural gas through the opening and closing control of the needle valve by a two-position two-way valve or a two-position three-way valve, so that multiple times of timely quantitative accurate injection of thecompressed natural gas can be realized; and the gas fuel injector continues a common rail injecting technology, is simple in structure and convenient to machine, and reduces the production cost.