Automatic　generation　control　(AGC)　is　very　important　to　power　system　operation.　But　for　reducing　its　action　number,　it　should　be　set　a　dead　band　for　governor,　as　a　result　to　increase　its　complexity.　In　this　paper　a　new　simulation　model　considering　the　effect　of　governor　dead　band　nonlinearity　by　using　the　describing　function　approach　for　automatic　generation　control　studies　of　two-area　system　is　proposed.　And　an　improvement　particle　swarm　optimization　algorithm　used　to　optimum　the　parameters　of　the　integral　controller　and　area　frequency　deviation　coefficient.　Through　the　simulation　analysis　of　the　automatic　generation　control　system　of　two-area　interconnected　power　system,　the　results　show　that　the　new　proposed　model　can　actually　enough　to　express　the　performances　of　the　automatic　generation　control　system,　and　that　this　method　is　effective.