Spin　polarization　in　an　InAs　quantum　dot　subjected　to　terahertz　(THz)　irradiation　and　external　magnetic　fields　is　theoretically　discussed.　Spin-polarized　oscillations　and　100%　spin　polarization　plateaus　are　obtained,　depending　on　the　relative　magnitude　between　the　external　magnetic　field　strength　and　the　THz　photon　energy.　Furthermore,　we　show　that　the　oscillation　of　spin　polarization　is　also　related　to　the　THz　irradiation　amplitude.　These　features　may　be　beneficial　for　low　magnetic　field　detectors,　ultrasensitive　THz　detectors　or　spin-selective　applications.