An implicit control-volume finite element method was proposed for simulation of injection molding, the time steps were controlled for both flow and thermal simulation by local flow information, and then the computing complexity analysis was conducted. The implicit scheme was based on updating the melt-air inter-face. The time steps of implicit algorithm were controlled by injection ratio and local mesh information of flow front to achieve "one time step, one element-layer" for filling simulation; the sub-time steps of computing temperatures were calculated for each node according to local courant number, and the thermal simulation was conducted by the filled order of nodes. Both analysis and case studies showed that the computing complexity of flow simulation was second-order of mesh size (nodal number) and one of thermal simulation was 1.5-order. As a result, the computing times and complexity of solving temperature were less than those of solving pressure. (c) 2006 Elsevier Ltd. All rights reserved.