The effective DC power modulation controller influences the security and stability of AC/DC interconnected power system significantly. Based on the direct feedback linearization model of parallel AC/DC transmission system, the DC power modulation controller is designed by using the dynamical adaptive sliding mode control designing method. Using an adaptive technique to estimate the switching control gain and damping coefficient, the dynamical sliding surface is proposed to eliminate tremble. The proposed adaptive sliding mode control scheme can be implemented without the requirement that the bounds of the uncertainties and the disturbances should be known in advance; meanwhile its design is very simple. The simulation results show that this proposed controller is superior to the nonlinear H∞ DC power modulation controller in damping oscillation and robustness.