I need help on converting the following sql command to a RelationPredicateBucket. I appreciate any help in advance.

SELECT * FROM Status order by SUBSTRING(StatusDesc, CHARINDEX('stsop', LOWER(StatusDesc), 0) + 5, 1000)

You can use nested DBFunctionCalls, there is an example in the following thread: http://www.llblgen.com/TinyForum/Messages.aspx?ThreadID=12051

Also you can use the DBFunctionCall with the constant feature as follows:

new DbFunctionCall( "SUBSTRING({0}, CHARINDEX('stsop', LOWER({0}), 0) + 5, 1000)", 
    new object[] { StatusFields.StatusDesc });

Thanks Walaa, But where I can fine DbFuncitonCall? (I mean in which assembly and namesapce).

DbFuncitonCall is part of the ORMSupportClasses assembly. Read the LLBLGenPro Help to figure out how to use such feature :

using SD.LlblGen.Pro.ORMSupportClasses;