A computationally efficient method that combines the subspace and projection separation approaches is proposed for 3-D frequency estimation of multiple sinusoids.From the perspective that 3-D sinusoids is a series of 2-D sliced matrices distributed in the third dimension

frequency parameters in the first dimension are estimated by applying the conventional MUSIC-based method to the covariance of the series of slice in the third dimension.Subsequently

a set of projection separation matrices is constructed to separate and estimate the frequency parameters in the second and the third dimension through a set of slices distributed in the third and the second dimension

respectively.The 3-D frequency parameters are automatically paired.For only the original scale of sampled data array is utilized

and the proposed method is more computationally attractive.Computer simulations show that the proposed algorithm is superior to IMDF and HOSVD methods of 3D case in terms of estimation performance and computational complexity.