can I use the value of field in last record?

I handle a output by a function with three parameters

the first is a value of Field [a1] in current record,

the second is value of Field [a1] in last record,

the third is value of Field [a1] in next record,

is it possible in RS2005?

Yes you can use them in a given scope (table/list):

Fields!a1.Value

Last(Fields!a1.Value, "Dataset1")

Fields!a1.Value(RowNumber("Dataset1")+1)

Shyam