No direct Taichung / Changhua / Miaoli to Green Island — go south via Kaohsiung on the South-Link Line, or HSR plus Puyuma Express to Taitung. Train, bus and ferry connections lined up.
From central Taiwan there is no direct service to Green Island; you either head south to Kaohsiung and take the South-Link Line to Taitung, or go north to Taipei and use the East Coast Line. Most travelers pick the southern route via Kaohsiung.
Taichung to Kaohsiung on an EMU3000 Tze-Chiang Limited Express takes about 2.5–3 hours; Kaohsiung to Taitung on an EMU3000 Tze-Chiang is about 1 hr 47 min at the fastest (slower services run closer to 3 hours). All-TRA end-to-end is about 5 hours. HSR to Zuoying then Puyuma Express / EMU3000 onwards comes out to about 3–3.5 hours total at roughly NT$1,200 — noticeably faster than all-TRA.
The Green Island route runs 2 fixed sailings on weekdays (09:30 and 13:30); in high season and on weekends and holidays it scales to 5 sailings a day (07:30 / 09:30 / 11:30 / 13:30 / 15:30).
A 06:00-ish all-TRA departure from Taichung gets you into Taitung after 13:00 — well past the 11:30 bus. The remaining 15:10 bus connects with the high-season 15:30 last sailing on a zero-buffer schedule, and on weekdays there is no boat at that hour. If you would rather not gamble, use HSR plus Puyuma Express / EMU3000 — that combination lines up cleanly with the 11:30 bus and the 13:30 weekday sailing.
If you cannot make it the same day, overnight in Taitung — stays around Taitung Train Station are plentiful — and aim for the 09:30 first sailing the next morning.
The South-Link Line is often suspended during typhoons or heavy rain (July–November); 2024 and 2025 both saw several major suspensions, so always check TRA announcements before you leave. Buy ferry tickets and confirm capacity on ferry.tw.