Vehicle platooning improves energy savings based on vehicle-to-vehicle (V2V) communication. The ecological cooperative adaptive cruise control (Eco-CACC) is implemented in platoons for merging task by using event-triggered and regrouped platoon model. The merging positions are selected in the middle and the tail of an original platoon with a two-vehicle sub-platoon. The distributed nonlinear model predictive controller (DNMPC) approach is developed to model Eco-CACC merging strategy. Performances of Eco-CACC merging strategy is modeled by leaders and predecessor-followers objectives control method for predecessor-leader following (PLF) topology. The results demonstrate that merging position located in the tail exhibits superior performances, which can be used to improve the string stability, tracking performance and communication stability.