Rashba spin splitting coefficients for the first two subbands1,2 and intersubband spin-orbit coupling coefficient 12 are obtained by projecting the characteristic equation into the subspace of conduction band. Then Schrdinger and the Poisson equations are solved self-consistently to calculate1,2 and 12 under different gate voltages. Then contributions to the spin-orbit coupling coefficients from the well, the left and the right heterointerfaces and the left and the right barriers of the quantum well are discussed. Resulsts show that the spin-orbit coupling coefficient can be modulated by the gate voltage, and the intersubband spin-orbit coupling coefficients calculated here are a little smaller than the Rashba coefficients1,2, but they are basically of the same order.