We investigate the electronic structure and magnetic properties of layered compound Sr3Fe2O5 based on first-principles calculations in the framework of density functional theory with GGA+U method.Under high pressure,the ladder-type layered structure of Sr3Fe2O5 is transformed into the infinite layered structure accompanied by a transition from G-type anti-ferromagnetic (AFM) insulator to ferromagnetic (FM) metal and a spin transition from S =2 to S =1.We reproduce these transformations in our calculations and give a clear physical interpretation.