static void Main(string[] args)

        {

            string[] name = new string[] { "景珍", "林惠洋", "成蓉", "洪南昌", "龙玉民", "单江开", "田武山", "王三明" };

            int[] score = new int[] { 90, 65, 88, 70, 46, 81, 100, 68 };

            int idax = 0;

            for (int i = 0; i < score.Length; i++)

            {

                idax += score[i];

            }

            int gg = idax / score.Length;

            Console.WriteLine("平均分是" + gg + ",高于平均分的有" + name);

            for (int i = 0; i < score.Length; i++)

            {

                if (score[i] > gg)

                {

                    Console.Write(name[i]+" ");

                }

            }

        }

首先，所有的Length都拼错了。

其次,WriteLine.

using System;
using System.Collections.Generic;
using System.Text;

namespace projAboveAvg
{
    class Program
    {
        static void Main(string[] args)
        {
            string[] name = new string[] {"景珍","林惠洋","成蓉","洪南昌","龙玉民","单江开","田武山","王三明"};
            int[] score = new int[] { 90, 65, 88, 70, 46, 81, 100, 68 };
            int sum=0,avg=0,x=0;
            for (int i = 0; i < score.Length; i++)
            {
                sum += score[i];
            }
            avg = sum / score.Length;
            Console.Write("平均分是" + avg+","+"高于平均分的有：");
            Console.WriteLine();
            for (int i = 0; i < score.Length; i++)
            {
                if (score[i] > avg)
                {
                    x = i;
                    Console.Write("{0} ", name[i]);   
                }
              
            }
          
        }
    }
}

Console.Write[i]("平均分是"+gg+",高于平均分的有"+name);

[i]多余了    Length  拼错了