全民健保開辦至今，面臨支出成長過於迅速的財務危機，相當多的改革方案因之被提出，其中之一是門診改採自負額制。本文建立一單期數學模型：假設政府在受到保財務收支損益平衡的限制、被保險人為風險趨避者、及其所得分布不均的狀況下，求取被保險人預期效用的最大，因而導得每位被保險人之最適門診年自負額約為新臺幣數千元。作者據此建議被保險人每年門診次數累計達五次、且累計金額超過4,000元，則健保始於給付，另配套減免低所得者的門診醫療費用。

　　　　　Twian's health expenditures have increased very rapidly since the implement of national health insurance program. Besides, the Bureau of National Health Insurance has thus faced severe financial crisis. A great number of reform proposals, including the scheme of outpatient deductible, have been proposed. A one-period mathematical model is set up in this study. The main layouts are (1) the insured have identical risk preference but different income; (2) the government subjects the financial break-even constraint to determine the premium rate; and (3) the government chooses the appropriate outpatient deductible in order to maximize the insured's expected utility. The simulation result shows that the optimal annual outpatient deductible is in the territory of several thousand N.T. dollars. The author therefore proposes that the insured are got paid if his/her annual accumulated outpatient expenses exceed N.T. $4,000 and the number of outpatient visits exceeds 5 times a year. In addition, the government should give additional monetary reduction on outpatient service for the low income insured.