要让fork的仓库与原仓库保持同步，主要有两种方法：

一、反向Pull Request

1、打开pull request

2、转换分支，让原仓库向你fork的仓库发出pull request请求

二、配置upstream指向fork的原仓库

1、查看现有的远程仓库：

$ git remote -v
origin  https://github.com/YOUR_USERNAME/YOUR_FORK.git (fetch)
origin  https://github.com/YOUR_USERNAME/YOUR_FORK.git (push)

2、添加指向原仓库的upstream：

$ git remote add upstream https://github.com/ORIGINAL_OWNER/ORIGINAL_REPOSITORY.git

3、查看origin和upstream

$ git remote -v
origin    https://github.com/YOUR_USERNAME/YOUR_FORK.git (fetch)
origin    https://github.com/YOUR_USERNAME/YOUR_FORK.git (push)
upstream  https://github.com/ORIGINAL_OWNER/ORIGINAL_REPOSITORY.git (fetch)
upstream  https://github.com/ORIGINAL_OWNER/ORIGINAL_REPOSITORY.git (push)

4、直接从原仓库的master分支拉取代码并直接合并代码，其中pull=fetch+merge.

git pull upstream master