Millimeter wave has great potential in the field of nondestructive testing due to its unique advantages of high resolution, high penetration and low photon energy. For the application of millimeter wave nondestructive testing, a three-dimensional imaging algorithm for nonuniform planar array was proposed by combining the idea of the range migration algorithm and the nonuniform fast Fourier transform. The proposed algorithm uses nonuniform fast Fourier transform to reconstruct the signal spectrum in wavenumber domain, which overcomes the limitation of nonuniform spatial sampling on traditional imaging algorithms based on Fourier transform. The proposed algorithm is aimed to eliminate the complicated interpolation operation and improve the imaging efficiency. In order to verify the effectiveness of the proposed algorithm, the back projection algorithm was used as a comparison, the simulation and experiment was carried out, respectively. Simulation and experimental results all show that the proposed algorithm can achieve high-efficiency imaging of dielectric targets with high imaging accuracy and fast speed.