An acoustic metal diaphragm comprises a diaphragm base made of an organic material and a metal-plated layer. The diaphragm base has a smooth surface. The metal-plated layer is adhered to the smooth surface of the diaphragm base by an intermediate layer. The intermediate layer is disposed between the diaphragm base and the metal-plated layer. The metal-plated layer is made of pure beryllium or a beryllium alloy. Accordingly, the diaphragm base is made of the organic material and provided with a smooth surface. The intermediate layer allows the metal-plated layer to be adhered to the smooth surface more firmly. Using the pure beryllium or beryllium alloy to manufacture the metal-plated layer increases the rigidity of the diaphragm base and maintains the softness thereof to slow down the attenuation of the bandwidth, attain a wider frequency band, solve the problem of the high frequency and increase the quality of the sound.