In this paper, a new pressure control scheme for a variable displacement pump is proposed under the consideration of various system uncertainties. The control design reported in this paper provides an effective approach for controlling the discharge pressure of variable displacement pumps to asymptotically track the desired pressure time history. With the provided nonlinear control design, the output pressure error dynamics are presented in a first order system with which the system performance is restricted by the limitations on control actuation, unmodeled dynamics, and parametric uncertainties. The discharge pressure overshoot is eliminated for the compensated closed-loop control system. On-line adaptive learning is introduced to compensate for the uncertainty in the pressure carry-over angle, which induces the most significant torque on the swashplate in a variable displacement pump. Experimental results are provided to validate the effectiveness of the proposed control approach.