AbstractSingle‐collector efficiency is of paramount importance in colloid filtration theory and widely used to represent the average filtration efficiency of a specific porous medium. In this work we present new formulations (unifying the stochastic and limiting trajectory cases) for efficient evaluation of the single‐collector efficiency with Lagrangian simulations in axisymmetric flow field for two commonly adopted particle‐releasing scenarios: from the envelope boundary (Happel sphere‐in‐cell) and from the upstream projected area (sphere‐in‐cylinder). We introduce an equivalent captured flux and define a capture indicator variable for each particle, to avoid calculation of local capture probability in previous studies. The single‐collector efficiencies obtained with the proposed formulations using particle trajectory simulations in axisymmetric flow field are in excellent agreement with full 3D simulation results, which validates our approach. The results are also compared with the Levich equation and published correlation equations. The differences between the two particle‐releasing scenarios are clarified and their impact on the single‐collector efficiency is quantified. The proposed axisymmetric simulation method can significantly reduce the computational time for obtaining single‐collector efficiency in comparison to 3D modeling approach, and can also be conveniently applied to studying particle transport in other practical scenarios involving axial symmetry, such as constricted tubes, impinging jet, stagnation‐point flow.