The invention provides an in-situ growth method of a germanium-gallium nanowire. The in-situ growth method comprises the following steps of mixing GaCl3, GeCl4 and an ionic liquid in the environment with the water oxygen content being lower than 2ppm to obtain an electrolyte; adopting a three-electrode electrochemical system including a working electrode, a counter electrode and a reference electrode to perform constant-voltage gallium electrodeposition on the electrolyte under the conditions of 55 to 65 DEG C and -1.4V to -1.6V, and obtaining a gallium nano-sphere on the surface of the working electrode; and continuously performing constant-voltage germanium electrodeposition growth under the conditions of 55 to 65 DEG C and -2V to -2.3V, and performing in-situ growth of the germanium-gallium nanowire on the surface of the working electrode. The germanium-gallium nanowire provided by the invention can improve the cycle performance and the rate capability of a battery of a pure germanium anode; and in addition, the in-situ growth method provided by the invention is simple to operate and low in cost.