The　sources　of　linewidth　measurement　uncertainty　of　AFM　type　P47　are　analyzed　in　details.　A　new　model　based　on　geometry　shape　of　linewidth　measurement　is　proposed.　An　uncertainty　evaluation　method　is　offered　according　to　systematic　analysis　results　in　linewidth　measurement.　The　measurement　uncertainty　component　caused　by　traditional　Si3N4AFM　tip　is　about　5%　of　the　total　linewidth.　Finally,　the　main　measurement　uncertainty　source-　AFM　tip　is　determined.