當固定資產沒有殘值時，依然可使用直線折舊法？

[直線折舊法]是計算折舊金額的一種, calculation:
每年折舊金額 = {[購入值] - [殘值]} / 折舊年份

殘值 (residual value) 是折舊後該資產剩餘的價值. For your question, it is YES, 因為固定資產沒有殘值依然可使用直線折舊法.

但若您是指其 淨值 (Net Asset Value = Cost - Accumulated Depreciation)是零, 則不需要再折舊.

Straight-line depreciation:

Straight-line depreciation is simple to understand: you take the depreciable cost (cost – salvage value殘值) of the asset and divide it by the asset’s useful life.

Each asset account will have its own associated accumulated depreciation account. The accumulated depreciation account has a credit balance, and since the account it is associated with is an asset account, it is a contra account, in this case a contra-asset account.

( Acquisition Cost - Salvage Value ) / Years of Useful Life

If this assets no have have salvage value, you cannot use this formula to calculate the depreciateion.

YOU CAN USED Declining-balance depreciation WHICH DOES NOT REQUIRE "SALVAGE VALUE IN CALCULATION!