Summary: The three-color continuous-variable entanglement directly produced by a cascaded nonlinear process in an optical superlattice was investigated theoretically. This cascaded nonlinear process can be realized by using quasi-phase-matching technique in a quasiperiodic superlattice. In the first step, signal- and idle-beams can be generated by a parametric down-conversion. Then, the third beam can be obtained through sum-frequency of idle and pump. The degree of quadrature phase amplitude correlations between the three modes was discussed by a sufficient inseparability criterion with a single inequality for continuous-variable entanglement.