DateTime old = DateTime.Now;
int date = 0;
date = (date | old.Year - 2000) << 4;
date = (date | old.Month) << 5;
date = (date | old.Day);
int time = 0;
time = (time | old.Hour) << 6;
time = (time | old.Minute) << 5;
time = (time | old.Second);
Int32 datetime = (date << 16) | time;

------解决方案--------------------
给你写出一个类，另一个你自己仿照着写就好了
C# code
        public class myDate
        {
            private ushort _value;  //  这个用于保存值

            public int Year    //  这个属性设置或读出年度码
            {
                set
                {
                    if (value <= 2099 || value >= 2000)
                    {
                        int temp = value % 100;
                        _value = (ushort)((temp << 9) | (_value & 0x1ff));
                    }
                }
                get { return (_value & 0xfe00) >> 9; }
            }

            public int Month    //  这个是月份
            {
                set
                {
                    if (value <= 12 || value >= 1)
                        _value = (ushort)((value << 5) | (_value & 0xfe1f));
                }
                get { return (_value & 0x1e0) >> 5; }
            }

            public int Day    //  这个是日期
            {
                set
                {
                    if (value <= 31 || value >= 1)
                        _value = (ushort)(value | (_value & 0xffe0));
                }
                get { return _value & 0x1f; }
            }

            public string Value    //  这个用于将指定格式的字符串装入本类对象，没做正确性检验的
            {
                set
                {
                    if (value.Length == 6)
                    {
                        Year = Int32.Parse(value.Substring(0, 2));
                        Month = Int32.Parse(value.Substring(2, 2));
                        Day = Int32.Parse(value.Substring(4, 2));
                    }
                }
            }
        }

------解决方案--------------------
应用myDate类的例子
C# code
        static void Main(string[] args)
        {
            myDate md=new myDate();
            md.Value = "121030";
            Console.WriteLine(md.Year);
            Console.WriteLine(md.Month);
            Console.WriteLine(md.Day);
        }