将ColumnFooter显示出来，并对相关属性做适当设置。 SetAggregationType接口可以帮助你方便的完成求和需求。

fpSpread1.Sheets[0].ColumnFooter.Visible = true;
fpSpread1.Sheets[0].ColumnFooter.RowCount = 2;
fpSpread1.Sheets[0].ColumnFooter.Columns[12].HorizontalAlignment = FarPoint.Win.Spread.CellHorizontalAlignment.Left; 
fpSpread1.Sheets[0].ColumnFooter.Cells[0, 12].RowSpan = 2; 

//Value

for (int r = 0; r < fpSpread1.Sheets[0].RowCount; r++)
{
    for (int j = 0; j < fpSpread1.Sheets[0].ColumnCount; j++) 
    {
        fpSpread1.Sheets[0].Models.Data.SetValue(r, j, j + r * fpSpread1.Sheets[0].ColumnCount); 
    }
}

int i = 0;

fpSpread1.Sheets[0].ColumnFooter.SetAggregationType(0,1, FarPoint.Win.Spread.Model.AggregationType.Sum);
fpSpread1.Sheets[0].ColumnFooter.Cells[0, i].Value = "Sum";