Abstract: An extension structure for a plastic molding portable memory product includes an outer casing unit, an inner sliding unit, and a closing unit. The inner sliding unit is positioned inside the outer casing unit, and can be extended by sliding, whereas the closing unit is combined with the outer casing unit to ensure the inner sliding unit will not slip out. The outer casing unit is produced using one body formation method that is free from the traditional method of combining two pieces of structures through high frequency wave compression work sequence to effectively increase product yield, reduce cost and improve the cosmetics.