Accessibility　has　drawn　extensive　attention　from　city　planners　and　transportation　researchers　for　decades.　With　the　benefits　of　large-scale　and　varying　time,　this　study　aims　to　combine　the　taxi　global　positioning　system　(GPS)　data　with　a　cumulative　opportunity　measure　to　calculate　taxi　accessibility　in　Beijing,　China.　As　traffic　conditions　vary　significantly　over　time　and　space,　we　select　four　typical　time　periods　and　introduce　a　grid-based　method　to　divide　the　study　area　into　grid　cells.　Both　the　GPS　signals　and　opportunities　that　include　the　constant　points　of　interest,　total　drop-offs,　and　dynamic　drop-offs,　are　aggregated　in　these　grid　cells.　The　cumulative　opportunity　measure　counts　all　reachable　grid　cells　within　the　given　travel　time　threshold,　along　with　the　corresponding　opportunities.　The　results　demonstrate　that　the　accessibility　varies　in　the　four　time　periods,　with　better　performance　seen　in　the　late-night　hours.　Although　the　spatial　distributions　of　the　three　kinds　of　opportunities　are　different,　these　accessibilities　show　great　similarity.　In　addition,　the　relative　accessibilities　of　different　measures　are　highly　correlated.　In　general,　grid　cells　with　higher　accessibilities　in　one　time　period　are　likely　to　also　have　higher　accessibilities　in　other　time　periods.　Moreover,　the　results　suggest　that　taxi　accessibility　can　be　measured　from　its　trajectory　data　only.