Your sample string doesn't contain any backslashes, you are just using it to mask the double quotes. This contains one backslash at the beginning and one at the end:
string s = "" teetete "";
If you want to replace it with a single double quote:
string t = s.Replace(""", """);
You have to look click at the loupe in the debugger to see the real value of a string:
与恶龙缠斗过久,自身亦成为恶龙;凝视深渊过久,深渊将回以凝视…