Herein, the first‐principles calculations in the framework of density functional theory (DFT) with generalized gradient approximation plus on‐site repulsion (GGA + U) are used to study the electronic structure and magnetic properties of NaxSr1−xFeO2. With different amounts of Na doping (x = 0.0625, x = 0.083, and x = 0.125), the crystal structure, magnetic structure, and electronic structure of the compounds are calculated and it is found that doping induces a transition from a high‐spin state to an intermediate‐spin state and from an antiferromagnetic (AFM) insulating state to a ferromagnetic (FM) half‐metallic state.