臺灣死亡率自日治時期以來快速下跌，平均餘命乃大幅上漲；死亡率下降過程中出現年齡分配變動的現象，下降的動力由早期嬰幼兒人口逐漸移入中高齡人口，晚近則高齡死亡率在年齡軸上趨平發展，使得平均餘命趨向極值與否成為討論的焦點。本文先使用人口粗死亡率的定義解析指出，年齡標準化的死亡水準雖然持續下降卻有趨緩的動向，對應著人口出生時平均餘命之趨緩成長，建立本文所要分析的事實基礎。接著引入文獻說明平均餘命之趨緩成長可能關聯著人類細胞分裂次數的限制，以及物競天擇的進化原理，使得「自然」死亡的年齡分配在40歲與已知最高歲數之間，而若最高齡的限制紋風不動，則死亡年齡分布的變異會因平均餘命增長而產生壓縮的現象。進一步使用區間餘命、死亡年齡分布變異數、人口熵、與Gompertz存活函數來檢討平均餘命趨向遲緩成長的原因，本文使用簡易生命表說明幼年及青壯人口的死亡率迫近自然下限，區間餘命迫近自然上限，使得平均餘命的成長動力轉為老年人口的死亡率改善；固然老年死亡率距離自然下限較遠，有較大幅度改善的空間，卻因長期累積致命風險與慢性疾病不容易治癒而較難改善，使得死亡水準下降與平均餘命的成長趨緩。接著使用完全生命表套入Gompertz存活函數以延伸年齡到100歲以上的單齡歲數，突破人口統計設定的最高齡組限制，並關聯死亡年齡分布的變異數與人口熵。分析結果發現平均餘命趨向遲緩成長的同時，死亡年齡分布的變異數與人口熵皆伴隨下降，而Gompertz存活函數的兩個主要參數也正好可以連結存活曲線的矩形化，指出臺灣人口的死亡年齡分布在高齡端117歲前後似乎形成一個牆角，因而產生死亡壓縮的現象。

Mortality in Taiwan has declined since 1920, and life expectancy has dramatically increased. This paper attempts to explain how the mortality decline and the increase in life expectancy have been slowing down. Adopting the notion of temporary life expectancy, it is shown that while the temporary life expectancies of those aged under 60 have approached the age interval as a natural upper limit, the main force of continued mortality decline shifted to the older age groups, and the momentum of mortality decline began to dwindle away. Applying Gompertz’s survival function l(x) = Abqx to the life table survivors lx in order to extend beyond the upper limit arbitrarily set up by the vital statistics, it is demonstrated that while b is simply A inverted, measuring the level of survival, the q parameter measures the steepness of the decline of survivors along with age. It is found that q is consistently related to Keyfitz’s entropy measure evaluated at age 0 and the variance of death numbers d(x) derived from the survival function l(x). All three measures moved south as the increase in life expectancy at birth kept slowing down. A mortality compression is obviously in place, hindering the continuing increase in life expectancy. It is suggested that the b and q parameters of the Gompertz survival function, as simple and natural as they are, can be applied to the examination of the rectangularization of the survival curve in place of the angle and other intriguing measurements.