In order to test concave aspherical surfaces precisely, a binary phase twin computer-generated hologram (CGH) is proposed and designed. The designed twin CGH consists of two segments, called main CGH and alignment CGH, used for testing aspherical surfaces and aligning main CGH respectively. The principle of testing aspherical surfaces is reviewed and the design method is introduced. Then a design example for testing a paraboloidal mirror (Φ140, F/2) is presented, and its root-mean-square (RMS) error is 0.062λ. The pattern distortion error of main CGH is derived from analyzing the errors of alignment CGH, and then the integrative error is 0.06λ. The validity of the test result is demonstrated and compared with that of autocollimation test, which is 0.062λ (RMS). It is demonstrated that the results show a good agreement.