A spatial-dependent robust control strategy is proposed for the on-ramp merging problem based on the coordination of the connected and automated vehicles. In the proposed strategy, the planning stage of the merging coordination is weakened while the control stage is strengthened. More specifically, the planning stage mainly forms a virtual platoon containing all vehicles inside the communication zone. In the control stage, the time-varying parameter uncertainties in the model are considered. A spatial-dependent controller with uniform boundedness, uniform ultimate boundedness and robustness is delicately designed for each vehicle in the virtual platoon to analytically calculate the control force in real time. The spatial-dependence means that the safety-related performances of the controller are directly and explicitly bonded with spatial locations such that the collision-avoidance safety is ensured at the most dangerous conflicting merging zone. Since spatial locations in the traffic environment are static, this spatial-dependence endows the proposed strategy more stability and reliability. The effectiveness of the proposed strategy is demonstrated through the verification, ablation and comparison simulation cases.