这个问题是因为国内网络无法正常下载 gradle 引起的，不管你是啥版本，都一样。
详细的错误如下：
[ +176 ms] Downloading https://services.gradle.org/distributions/gradle-6.7-all.zip [+5206 ms] Exception in thread "main" java.net.SocketException: Connection reset [ ] at java.net.SocketInputStream.read(SocketInputStream.java:210) [ ] at java.net.SocketInputStream.read(SocketInputStream.java:141) [ ] at sun.security.ssl.InputRecord.readFully(InputRecord.java:465) [ ] at sun.security.ssl.InputRecord.read(InputRecord.java:503) [ ] at sun.security.ssl.SSLSocketImpl.readRecord(SSLSocketImpl.java:983) [ ] at sun.security.ssl.SSLSocketImpl.performInitialHandshake(SSLSocketImpl.java:1385) [ ] at sun.security.ssl.SSLSocketImpl.startHandshake(SSLSocketImpl.java:1413) [ ] at sun.security.ssl.SSLSocketImpl.startHandshake(SSLSocketImpl.java:1397) [ ] at sun.net.www.protocol.https.HttpsClient.afterConnect(HttpsClient.java:559) [ ] at sun.net.www.protocol.https.AbstractDelegateHttpsURLConnection.connect(AbstractDelegateHttpsURLConnection.java:185) [ ] at sun.net.www.protocol.http.HttpURLConnection.getInputStream0(HttpURLConnection.java:1564) [ ] at sun.net.www.protocol.http.HttpURLConnection.getInputStream(HttpURLConnection.java:1492) [ ] at sun.net.www.protocol.https.HttpsURLConnectionImpl.getInputStream(HttpsURLConnectionImpl.java:263) [ ] at org.gradle.wrapper.Download.downloadInternal(Download.java:58) [ ] at org.gradle.wrapper.Download.download(Download.java:44) [ ] at org.gradle.wrapper.Install$1.call(Install.java:61) [ ] at org.gradle.wrapper.Install$1.call(Install.java:48) [ ] at org.gradle.wrapper.ExclusiveFileAccessManager.access(ExclusiveFileAccessManager.java:65) [ ] at org.gradle.wrapper.Install.createDist(Install.java:48) [ ] at org.gradle.wrapper.WrapperExecutor.execute(WrapperExecutor.java:128) [ ] at org.gradle.wrapper.GradleWrapperMain.main(GradleWrapperMain.java:61) [ +3 ms] Running Gradle task 'assembleDebug'… (completed in 5.4s) [ ] [!] Gradle threw an error while downloading artifacts from the network. Retrying to download… [ +4 ms] Exception: Gradle task assembleDebug failed with exit code 1 [ +2 ms] "flutter run" took 15,740ms.
这是因为我们在 android/gradle/wrapper/gradle-wrapper.properties 文件中指定从 distributionUrl 下载 gradle，一般是从 gradle 官网下载，如： https://services.gradle.org/distributions/gradle-6.7-all.zip，但是国内网络无法从这个地址下载，就会导致上面的问题，不管你指定的是 gradle 6.0 还是 6.7 还是别的版本。
解决办法：使用国内的地址，如下，
distributionUrl=https\://code.aliyun.com/kar/gradle-all-zip/raw/master/gradle-6.7-all.zip