再保險的功能在於危險分散，而保險公司對於所承接的業務往往僅針對過去所習慣使用的再保險方式來評估該業務的自留額度，但卻很少考慮不同再保險方式的比較對自留額水準的影響，來調整其再保險策略。由於國內壽險公司長期以來習於運用比例性再保險（Proportional Reinsurance）方式將大量業務轉分給再保險人，雖從中賺取豐碩再保佣金，卻也限制資本規模累積與技術的提升，同時有可能喪失應保有的簽單核保利潤。本文以K保險公司之團體傷害保險業務為例，檢視業務由比例性再保險（Proportional Reinsurance）之溢額再保險（Surplus Reinsurance）方式轉換為非比例性再保險（Non-Proportional Reinsurance）之普通超額賠款再保（Working Excess of Loss Cover；簡稱 WXL）方式，評估再保險方式轉換之可行性，文中最主要考量的觀點為再保損失分攤與再保損益，損失分攤的部分係運用破產機率理論，在不改變現行溢額再保險自留額水準前提下，決定K保險公司可支配之自由運用資金，再依此一可支配自由運用資金決定轉換後再保方式之最適自留額度；而再保損益的部份係在不影響原來可分配於該自留業務的可自由運用資金前提下，以實際再保收支情形估算轉換後之再保方式是否可為保險公司減少再保損失。結果發現該保險公司之團體傷害保險業務若採用轉換後之再保方式（即超額賠款再保方式）確實可為該公司帶來降低再保險成本之效益。筆者希望藉由本研究建議保險公司對於再保風險評估除了自留額度估算之外，同時對於再保險方式的選擇也應重視。 The main function of reinsurance is to share risks . Normally the insurance company is seldom to adjust its reinsurance strategy by considering the impact of the various reinsurance types to the level of retention, but follow its past experience rules to determine it. A persisting practice that the domestic insurance companies follow the rule of proportional reinsurance to cede the “business” to the reinsurance companies is to limit its capital growth as well as to jeopardize the underwriting profit deserved, though there is high commission of reinsurance paid back. Through a case study to group personal accident insurance business of “K” Company, this dissertation discussed the affections of retention limit under transformation from surplus treaty of proportional reinsurance to WXL of non-proportional reinsurance. The main perspectives here are loss sharing for risks and possible loss saving of reinsurance operation. For loss sharing, the author determined the free reserves permitted under the original surplus treaty through ruin theory, then set a proper retention limit for the objective treaty ----- working excess of loss cover. And the author then compared the loss savings of reinsurance operation between the treaties above by setting the same free reserves permitted. The conclusion is that if the Company adapts working excess of loss for the group personal accident insurance business, it is proved that the transformation can reduce the cost of reinsurance operation without bothering the function of sharing risks of reinsurance. Therefore, the author would like to suggest the insurance company not only to care the retention limits of reinsurance, but also select the proper types of reinsurance.