An efficient algorithm is proposed for eliminating the requirement of coherent sampling in multi-tone spectral test of ADCs. Instead of repetitively performing the single-tone non-coherency correction algorithms, the proposed method simultaneously corrects all non-coherent input signal tones to be coherent, which improves the algorithmic reliability and efficiency greatly. Theoretical analysis and simulation results demonstrate that the developed method can achieve the same test accuracy and equivalent efficiency as the coherent sampling method in both wide and narrow tone spacing cases. Comparative studies from the windowing techniques and the single-tone non-coherency correction methods validate the test accuracy, reliability and efficiency of the proposed method.