To reasonably allocate shared resources (SRs) in project portfolios (PP) and realize PP's maximal benefits, in this article, we propose a hybrid SRs allocation model based on system dynamics (SD) and discrete event simulation (DES). Unlike previous resource allocation methods that solely consider project level benefits, the proposed model simultaneously considers the benefits at both project and portfolio levels. Specifically, starting from the project activity level, we first construct a project schedule evaluation submodel using DES; second, a synergy benefit evaluation submodel at the portfolio level is constructed by considering both the positive and negative benefits brought by SRs allocation using SD; finally, by clarifying the connection between the two submodels, a hybrid simulation model for SRs allocation is obtained. A case study is used to demonstrate the practicality of the hybrid model. Sensitivity analysis is then conducted to examine how the model output changes due to variations in parameters. The proposed model is also compared with the DES model to demonstrate the superiority of the hybridization. Simulation results reveal that the proposed model can systematically integrate the effects of SRs allocation at both project and portfolio levels, which provides PP managers a tool to enhance SRs allocation performance.