實務上稅法都有核課期間的規定，因此本文將核課期間納入考慮並探討其存在對納稅人逃漏稅行為的影響，文中並對現行稅法規定提供政策建議。研究顯示：(1) 忽略核課期間的考慮會高估逃漏稅的程度，因而會低估政府的預期稅收；此一結果似乎可用來解答為何實務上觀察到的租稅逃漏稅程度遠比理論模型所預測的輕微這個困惑。(2) 與傳統租稅逃漏模型相較，考慮核課期間後，納稅人的預期效用水準較低。導致上述結果的主要原因在於，核課期間的引入將使得納稅人在進行租稅逃漏時，其所得在此一期間內處於不確定的狀態，因而影響到納稅的消費決策所致。此外，本文亦對於實務上納稅人面對相同核課期間的規定提供一個政策建議。 Conventional literatures neglect the influence of the tax assessment period on evasion. This paper explores their relationships and provides some policy suggestions. When tax assessment period is considered, tax compliance rate is higher, government revenue is more and taxpayer’s utility level is lower than those in traditional models. Thus it offers an explanation about “the puzzle of tax evasion”, which says the actual evasion is far less serious than predicted in conventional literatures. The main reason for above results is that taxpayer’s disposable income is uncertain during the assessment period and thereby influences his consumption as well as tax evasion decisions. Besides, as all taxpayers facing identical assessment period, this paper provides a policy suggestion with Pareto improving characteristics.