I have three string called This_is string1 and This is string2 There_is string3
This_is string1
This is string2
There_is string3
How to split these 3 strings after \"This_\", \"T
So you want to split only the first part? You can use the overload of String.Split that allows to specify the count and multiple delimiters:
str.Split(new[]{' ', '_'}, 2);
So on the first string you get: "This" + "is string1", similar on the others.
"This"
"is string1"