1.第一步：

npm install sass-resources-loader --save-dev

2.然后在build 的utils.js中exports.cssLoaders = function (options) {}中加上一下代码：

function lessResourceLoader() {
        var loaders = [
            cssLoader,
            'less-loader',
            {
                loader: 'sass-resources-loader',
                options: {
                    resources: [
                        path.resolve(__dirname, '../src/assets/styles/common.less'),
                    ]
                }
                        }
        ];
        if (options.extract) {
            return ExtractTextPlugin.extract({
                use: loaders,
                fallback: 'vue-style-loader'
            })
        } else {
            return ['vue-style-loader'].concat(loaders)
        }
    }

path.resolve(__dirname, '../src/style/style.less')路径改成自己对应的文件
然后后面将 return{} 块中的 less: generateLoaders('less') 替换成上面自定义的函数 less: lessResourceLoader()

结果如下

exports.cssLoaders = function (options) {
  options = options || {}

  const cssLoader = {
    loader: 'css-loader',
    options: {
      sourceMap: options.sourceMap
    }
  }

  var postcssLoader = {
    loader: 'postcss-loader',
    options: {
      sourceMap: options.sourceMap
    }
  }

  function lessResourceLoader() {
    var loaders = [
      cssLoader,
      'less-loader',
      {
        loader: 'sass-resources-loader',
        options: {
          resources: [
            path.resolve(__dirname, '../src/style/style.less'),
          ]
        }
      }
    ];
    if (options.extract) {
      return ExtractTextPlugin.extract({
        use: loaders,
        fallback: 'vue-style-loader'
      })
    } else {
      return ['vue-style-loader'].concat(loaders)
    }
  }

  // generate loader string to be used with extract text plugin
  function generateLoaders (loader, loaderOptions) {
    const loaders = options.usePostCSS ? [cssLoader, postcssLoader] : [cssLoader]
    if (loader) {
      loaders.push({
        loader: loader + '-loader',
        options: Object.assign({}, loaderOptions, {
          sourceMap: options.sourceMap
        })
      })
    }

    // Extract CSS when that option is specified
    // (which is the case during production build)
    if (options.extract) {
      return ExtractTextPlugin.extract({
        use: loaders,
        fallback: 'vue-style-loader'
      })
    } else {
      return ['vue-style-loader'].concat(loaders)
    }
  }

  // https://vue-loader.vuejs.org/en/configurations/extract-css.html
  return {
    css: generateLoaders(),
    postcss: generateLoaders(),
    less: lessResourceLoader('less'),
    sass: generateLoaders('sass', { indentedSyntax: true }),
    scss: generateLoaders('sass'),
    stylus: generateLoaders('stylus'),
    styl: generateLoaders('stylus')
  }
}

修改完配置文件记得重启服务器：npm run dev
ok, style.less如下:

@sidebar:240px;
@headerHeight:65px;
@bodyMinWidth: 700px;

注意，赋值不是等号
在组件中，就可以使用全局变量了。

  .content {
    background:red;
    height:auto;
    margin-left: @sidebar;
    width: calc(100%-@sidebar);
  }
</style>

好用！