Abstract: An adaptive implicit algorithm was proposed for RTM mold filling simulation. The proposed implicit algorithm was based on the update of the interface in order to track the flow front.The governing equations of the filled nodes were solved to obtain the pressure distribution, and filling fractions of the front nodes were checked to determine if any node is needed to be added to the filled nodes or be removed from the filled nodes. Based on the criterion that the resin moves forward only one element-size distance at each time step, the Recursive Least Square (RLS) adaptive method was employed dynamically to update the time step. The half-filled time of control volumes was estimated by the pressures in order to construct the flow fronts at any given time. The case studies demonstrate that the adaptive implicit algorithm improves the performance and flexibility of the implicit algorithm. The computational time complexity of 2.5D is reduced to 2 order of the node number.