The fast and accurate computation of the static and dynamic characteristics is the foundation of design and optimization of electromagnetic (EM) relay. This paper, considering the advantages of both the magnetic equivalent circuit (MEC) method and the finite element method (FEM) for the EM system computation, proposes an algorithm of output space-mapping (OSM) based on the compensation factor (CF). This algorithm, based on the differentiability of CF function about dimensional parameters, can attain the fast and accurate computation of the static and dynamic characteristics of the EM relay, when the dimensional parameters vary within their ranges, respectively. The comparison of the static attraction torque and dynamic characteristics computing by the OSM algorithm and FEM shows that the OSM algorithm is reliable.