A novel robust adaptive beamforming algorithm based on coprime array is proposed in this paper. First, we exploit the virtual array structure of coprime coarray to construct two subspaces. The first subspace is obtained from the covariance matrix of the virtual uniform linear array, whereas the second one is obtained by integrating spatial spectrum over each angular sector of signal. Then, by using a closed-form expression of projection-based approach, the steering vectors of signals are estimated from the intersection of the two subspaces. Moreover, according to the covariance fitting theory, the power associated with the desired signal, interference signals and noise is obtained from the virtual sample covariance matrix. In addition, to reconstruct interference-plus-noise covariance matrix (INCM), the maximum correlation principle is used to transfer the virtual SVs of signals to real ones corresponding to a physical array. Finally, with the estimated the SV of the desired signal and the INCM, the proposed robust algorithm is devised. Simulation results demonstrate the superiority and effectiveness of the proposed algorithm.