The invention provides a manufacturing method for a CMOS transistor with a dual work function metal gate. The method involves forming gate materials with different thickness in different MOS areas, then introducing metal aluminum as metal for adjusting a work function, and through an annealing process, by using the characteristics that a lower work function can be obtained through an A1 staying at a gate layer and a higher work function can be obtained through the A1 entering a gate insulation layer, the dual work function metal gate of the CMOS can be realized, and the integration process of the dual work function metal gate is simplified.