目前程式碼

string sDIS_BEGIN_DATE = "10701011100";
string sDIS_END_DATE = "10712251100";
DateTime dDIS_BEGIN_DATE = DateTime.ParseExact(sDIS_BEGIN_DATE, "yyyMMddHHmm", System.Globalization.CultureInfo.InvariantCulture);
DateTime dDIS_END_DATE = DateTime.ParseExact(sDIS_END_DATE, "yyyMMddHHmm", System.Globalization.CultureInfo.InvariantCulture);
                    
var dis_L = (from t1 in db.xxx
                             where t1.dDIS_XXX >= dDIS_BEGIN_DATE
                                && t1.dDIS_XXX <= dDIS_END_DATE
                             orderby t1.dDIS_XXX descending
                             select t1).ToList();

找出來的資料是無,資料庫內資料有3個(想要找到這3個)
字串轉dateTime有甚麼其他的方式嗎?

最後解答：
因字串為民國年，首先轉成西元年字串，再用DateTime.ParseExact 轉成DateTime
先取出字串前三碼，用INT+1911，在組回字串，最後轉型態DateTime以供LINQ查詢使用
解答程式碼

string sDIS_BEGIN_DATE = "10701011100";
string sDIS_END_DATE = "10712251100";
DateTime dDIS_BEGIN_DATE = AYDateTime.GetTwdate(sDIS_BEGIN_DATE,"yyyyMMddHHmm");
DateTime dDIS_END_DATE = AYDateTime.GetTwdate(sDIS_END_DATE, "yyyyMMddHHmm");
                    dis_L = (from t1 in db.XXX
                             where t1.dDIS_XXX >= dDIS_BEGIN_DATE
                                && t1.dDIS_XXX <= dDIS_END_DATE
                             orderby t1.dDIS_XXX descending
                             select t1).ToList();
                             
 //把運算公式整合成函數以供日後使用
 public static DateTime GetTwdate(string sValue, string sFormat)
        {
            int iADNum = 1911;
            return DateTime.ParseExact((int.Parse(sValue.Substring(0, 3)) + iADNum) + sValue.Substring(3), sFormat, System.Globalization.CultureInfo.InvariantCulture);
        }

補充：函數內的參數sFormat可以預設格式，假如你已經固定那些格式，如下

public static DateTime GetTwdate(string sValue)
        {
            int iADNum = 1911;
            string[] sFormat = { 
                            "yyyy/M/d tt hh:mm:ss", 
                            "yyyy/MM/dd tt hh:mm:ss", 
                            "yyyy/MM/dd HH:mm:ss", 
                            "yyyy/M/d HH:mm:ss", 
                            "yyyy/M/d", 
                            "yyyy/MM/dd" 
                        }; 
            return DateTime.ParseExact((int.Parse(sValue.Substring(0, 3)) + iADNum) + sValue.Substring(3), sFormat, System.Globalization.CultureInfo.InvariantCulture);
        }