激活 4 分钟· 更新于 2026-10-16
如何用产品密钥激活 Office 2021（或 2019）
setup.office.com 绑定、应用内激活，以及常见的"此密钥已被使用"错误解析。
Office activation depends on the key type you bought. There are two flows — and mixing them up is the #1 cause of activation problems.
Flow A: Keys that bind to a Microsoft account (setup.office.com)
- •Go to setup.office.com and sign in with a Microsoft account
- •Enter the 25-character key — it binds permanently to that account
- •Office downloads/activates automatically; reinstalls later only need the account login, not the key
- •The key is consumed once — it can never be used on a different account
Flow B: In-app / MAK keys
- •Open Word → File → Account → Change License / Activate Product
- •Enter the key → activate online
- •MAK keys on a closed network can use phone activation (same slui 4 flow as Windows)
Common problems
| Symptom | Cause | Fix |
|---|---|---|
| "Key already used" | Bind-type key redeemed on a different Microsoft account | Sign in with the account it was bound to — the key cannot move |
| "This key isn't for this product" | Edition mismatch (e.g., ProPlus key vs Home&Business installer) | Install the matching edition — check the key in our PID Checker |
| Unlicensed product banner after install | Multiple Office versions installed side-by-side | Remove the old version, run online repair |
| Activation works, then reverts | Subscription check on a 365 install, or leftover trial license | osa /fix or remove the trial license in Account → Manage Licenses |
Before you redeem
Decide which Microsoft account should own the key BEFORE entering it at setup.office.com — the binding is permanent and Microsoft support cannot move it.