A blind audio watermark embedding algorithm by a holographic technique was proposed. The digital-watermark image to be hidden was phase modulated in a random wise in order to form the object wave. The Fourier transform of the object wave was interfered with the reference wave to form the Fourier-transformed digital hologram. It made full use of the energy compression of DCT (Discrete Cosine Transform) to embed the watermark,in the form of Fourier-transformed digital hologram,into the audio signal by quantification process. The watermark can be extracted without the original audio signal. The process of constructing and reconstructing a digital hologram were described on the basis of the theory of Fourier optics and simulated by the computer. Experimental results show that the algorithm was robust against common signal manipulations and attacks,such as Gaussian noise,low pass filter and cropping especially.