grunt.registerTask('default',['concurrent']);

你配置的最后一行应该是：

grunt.registerTask('default',['concurrent:target']);

不知道你的问题有没有解决 我也遇到了一样的问题：

这是完整的配置代码：

module.exports = function(grunt) {

  grunt.initConfig({
    watch: {
      jade: {
        files: ['views/**'],
        options: {
          livereload: true
        }
      },
      js: {
        files: ['public/js/**', 'models/**/*.js', 'schemas/**/*.js'],
        //tasks: ['jshint'],
        options: {
          livereload: true
        }
      },
      uglify: {
        files: ['public/**/*.js'],
        tasks: ['jshint'],
        options: {
          livereload: true
        }
      },
      styles: {
        files: ['public/**/*.less'],
        tasks: ['less'],
        options: {
          nospawn: true
        }
      }
    },

    jshint: {
      options: {
        jshintrc: '.jshintrc',
        ignores: ['public/libs/**/*.js']
      },
      all: ['public/js/*.js', 'test/**/*.js', 'app/**/*.js']
    },

    less: {
      development: {
        options: {
          compress: true,
          yuicompress: true,
          optimization: 2
        },
        files: {
          'public/build/index.css': 'public/less/index.less'
        }
      }
    },

    uglify: {
      development: {
        files: {
          'public/build/admin.min.js': 'public/js/admin.js',
          'public/build/detail.min.js': [
            'public/js/detail.js'
          ]
        }
      }
    },

    nodemon: {
      dev: {
        options: {
          file: 'app.js',
          args: [],
          ignoredFiles: ['README.md', 'node_modules/**', '.DS_Store'],
          watchedExtensions: ['js'],
          watchedFolders: ['./'],
          debug: true,
          delayTime: 1,
          env: {
            PORT: 3000
          },
          cwd: __dirname
        }
      }
    },

    mochaTest: {
      options: {
        reporter: 'spec'
      },
      src: ['test/**/*.js']
    },

    concurrent: {
      tasks: ['nodemon', 'watch', 'less', 'uglify', 'jshint'],
      options: {
        logConcurrentOutput: true
      }
    }
  })

  grunt.loadNpmTasks('grunt-contrib-watch')
  grunt.loadNpmTasks('grunt-nodemon')
  grunt.loadNpmTasks('grunt-concurrent')
  grunt.loadNpmTasks('grunt-mocha-test')
  grunt.loadNpmTasks('grunt-contrib-less')
  grunt.loadNpmTasks('grunt-contrib-uglify')
  grunt.loadNpmTasks('grunt-contrib-jshint')

  grunt.option('force', true)

  grunt.registerTask('default', ['concurrent'])

  grunt.registerTask('test', ['mochaTest'])
}

我已经按照你的方法执行了，但报错还是存在。

这是我的Gruntfile.js配置内容:

module.exports = function(grunt) {
    grunt.initConfig({
        watch : (省略),
        nodemon : (省略), 
        concurrent: {
          target: {
            tasks: ['nodemon', 'watch'],
            options: {
              logConcurrentOutput: true
            }
          }
        }
    })
    
    grunt.loadNpmTasks('grunt-contrib-watch');
    grunt.loadNpmTasks('grunt-nodemon');
    grunt.loadNpmTasks('grunt-concurrent');
    
    grunt.option('force',true);
    grunt.registerTask('default',['concurrent']);
}

但是不管我在npm里执行grunt，还是grunt concurrent。都报错No "concurrent" targets found.

npm install grunt-concurrent --save

留意一下，是否能安装成功。

直接 grunt concurrent 是需要你先注册，也就是 registerTask 一个 grunt task 名字，然后才能在命令行里调用