How to access external DLL's static methods that incorporate output parameters in SQL Server
What have you tried and what error are you getting?

The following works for me on SQL Server 2008 R2.

C#:

namespace CLRTest
{
    public static class ParamsTest
    {
        [SqlProcedure]
        public static void Test(out int p)
        {
            p = 5;
        }
    }
}


SQL:

CREATE PROCEDURE dbo.Test(@p int OUTPUT)
    AS EXTERNAL NAME [CLRTest].[CLRTest.ParamsTest].[Test];
GO


DECLARE @x int;

EXEC dbo.Test @p = @x OUTPUT;

SELECT @x;


Returns 5 as expected.



Now, if you're trying to return an array in an output parameter, I don't think that's supported, save for the exceptions noted here. If that's what you're looking to do, use a table-valued function or stored procedure to return a result set. Note also that table-valued (input) parameters are not supported as mentioned here, assuming you're using SQL Server 2008 or higher.