官方标准安装方法：

$ brew tap dart-lang/dart
$ brew install dart

但是执行第二步会出错：

==> Installing dart from dart-lang/dart
==> Downloading https://storage.googleapis.com/dart-archive/channels/stable/release/2.0.0/sdk/dartsdk-macos-x64-release.zip

curl: (35) LibreSSL SSL_connect: SSL_ERROR_SYSCALL in connection to storage.googleapis.com:443
Error: An exception occurred within a child process:
DownloadError: Failed to download resource “dart”
Download failed: https://storage.googleapis.com/dart-archive/channels/stable/release/2.0.0/sdk/dartsdk-macos-x64-release.zip

原因可能是墙，也可能是服务器问题。单独下载https://storage.googleapis.com/dart-archive/channels/stable/release/2.0.0/sdk/dartsdk-macos-x64-release.zip
几乎走不动。
从这儿下载：
https://download.csdn.net/download/dreamfine/10734968
然后解压就行了，随便你放在哪儿，在Dart IDE，如webstorm中, 指定SDk位置就行了。