The　3003　aluminum　alloy　was　deformed　by　isothermal　compression　in　the　range　of　deformation　temperature　300-500　degrees　C　at　strain　rate　0.01-10.0　s(-1)　with　Gleeble-1500　thermal　simulator.　A　constitutive　equation　is　established　from　the　flow　stress　of　the　hot　deformation.　It　is　found　that　the　average　grain　size　of　the　3003　aluminum　alloy　increases　with　the　decrease　of　Zener-Hollomon　(Z)　value,　and　there　is　a　linear　correlation　between　them.　The　prediction　model　of　the　steady-state　flow　stress　and　the　average　grain　size　is　established.　The　steady-state　flow　stress　increases　with　the　decrease　of　the　average　grain　size.　The　microhardness　of　the　3003　aluminum　alloy　has　a　positive　linear　relationship　with　lnZ,　and　the　relationship　between　the　microhardness　and　the　grain　size　meets　the　Hall-Petch　equation,　which　can　provide　a　reference　for　the　microstructure　control　and　rolling　equipment　selection　of　the　3003　aluminum　alloy　under　hot　deformation　conditions.