The　coherence　of　light　source　have　been　employed　in　many　aspects,　such　as　optical　processing　and　optical　coherence　holography.　For　this　reason　it　has　attracted　vast　interest　in　developing　quantitative　methods　for　measuring　the　spatial　coherence　characteristics　of　an　optical　field.　We　propose　a　novel　method　for　measuring　the　spatial　coherence　degree　of　optical　fields　based　on　the　triangular　interferometer.　Spatially　separated　twin　beams　are　formed　by　an　interferometer,　and　the　interferogram　formed　by　the　twin　beams　is　captured　by　an　image　detector.　Because　the　separation　of　the　twin　beams　is　related　to　the　coordinate　position　of　the　input　beam,　a　series　of　positions　are　sampled　by　moving　a　pinhole　and　corresponding　interference　patterns　are　recorded.　Then　the　visibilities　of　the　interference　patterns　are　calculated　for　measuring　the　spatial　coherence　degree.　Experimentally　measured　and　theoretically　calculated　values　of　spatial　coherence　degree　fit　well.　The　measurement　error　is　3.8%.　Experimental　results　show　the　method　proposed　here　is　effective,　simple,　and　robust　without　any　special　optical　elements.