The free surface and unrotational-symmetric surface optical elements have been applied more and more widely along with the development of optical design technology, although they are still difficult for manufacturing. In this letter, a SiC unrotational-symmetric aspheric surface whose surface equation is z=3\lambda(x3+y3)(\lambda=0.6328 \mum) has been introduced. The tilt abstraction is adopted to minimize the material removal. The surface figures are peak-to-valley (PV) value of 0.327\lambda and root-mean-square (RMS) value of 0.023\lambda. A non-null testing method based on digital mask is proposed to test this surface. The accuracy of the method is testified by the experiment of standard sphere testing.