三，解决问题

方法一：修改配置文件

1，找到Untiy安装目录下的AndroidPlayer\Tools\GradleTemplates文件夹下的 baseProjectTemplate.gradle 文件

参考我的目录：
D:\Program Files\Unity\2019.4.19f1c1\Editor\Data\PlaybackEngines\AndroidPlayer\Tools\GradleTemplates

// GENERATED BY UNITY. REMOVE THIS COMMENT TO PREVENT OVERWRITING WHEN EXPORTING AGAIN

allprojects {
    buildscript {
        repositories {**ARTIFACTORYREPOSITORY**
            google()
            jcenter()
        }

        dependencies {
            // If you are changing the Android Gradle Plugin version, make sure it is compatible with the Gradle version preinstalled with Unity
            // See which Gradle version is preinstalled with Unity here https://docs.unity3d.com/Manual/android-gradle-overview.html
            // See official Gradle and Android Gradle Plugin compatibility table here https://developer.android.com/studio/releases/gradle-plugin#updating-gradle
            // To specify a custom Gradle version in Unity, go do "Preferences > External Tools", uncheck "Gradle Installed with Unity (recommended)" and specify a path to a custom Gradle version
            classpath 'com.android.tools.build:gradle:3.4.0'
            **BUILD_SCRIPT_DEPS**
        }
    }

    repositories {**ARTIFACTORYREPOSITORY**
        google()
        jcenter()
        flatDir {
            dirs "${project(':unityLibrary').projectDir}/libs"
        }
    }
}

task clean(type: Delete) {
    delete rootProject.buildDir
}

修改为：

// GENERATED BY UNITY. REMOVE THIS COMMENT TO PREVENT OVERWRITING WHEN EXPORTING AGAIN

allprojects {
    buildscript {
        repositories {**ARTIFACTORYREPOSITORY**
            //google()
            //jcenter()
           maven{ url 'http://maven.aliyun.com/repository/google'}           
           maven{ url 'http://maven.aliyun.com/repository/gradle-plugin'}
           maven{ url 'http://maven.aliyun.com/nexus/content/groups/public/'}
           maven{ url 'http://maven.aliyun.com/repository/jcenter'}

        }

        dependencies {
            // If you are changing the Android Gradle Plugin version, make sure it is compatible with the Gradle version preinstalled with Unity
            // See which Gradle version is preinstalled with Unity here https://docs.unity3d.com/Manual/android-gradle-overview.html
            // See official Gradle and Android Gradle Plugin compatibility table here https://developer.android.com/studio/releases/gradle-plugin#updating-gradle
            // To specify a custom Gradle version in Unity, go do "Preferences > External Tools", uncheck "Gradle Installed with Unity (recommended)" and specify a path to a custom Gradle version
            classpath 'com.android.tools.build:gradle:3.4.0'
            **BUILD_SCRIPT_DEPS**
        }
    }

    repositories {**ARTIFACTORYREPOSITORY**
        //google()
        //jcenter()
        maven{ url 'http://maven.aliyun.com/repository/google'}           
        maven{ url 'http://maven.aliyun.com/repository/gradle-plugin'}
        maven{ url 'http://maven.aliyun.com/nexus/content/groups/public/'}
        maven{ url 'http://maven.aliyun.com/repository/jcenter'}

        flatDir {
            dirs "${project(':unityLibrary').projectDir}/libs"
        }
    }
}

task clean(type: Delete) {
    delete rootProject.buildDir
}

然后重新打包即可。

方法二：修改Preferences属性

在官网上提前下载好需要版本gradle：https://gradle.org/releases/
然后在Preferences面板上，将Gradle Installed…选项前面√取消勾选，然后点击“Browse”，找到自己下载好的gradle，然后重新打包就可以了。