The self-affine measures is decided by {Φd(x) = M-1(x + d)}deD. When M ∈ Mn(Z),M = [adbc]D = {(00),(10),(20),(11)}, and ac - bd ∈ 2Z , by discussing the properties of the zero points of the self-affine measure's fourier transform, the number of orthogonal exponentials in a special L2 (μM,D) space is obtained.