本文從傳世文獻對「六畜」的五行配屬談起，並逐一分析《日書》中牲畜良、忌日所透露出來的五行性質及其選擇原則。從傳世文獻的整理來看，六畜的五行配屬並沒有固定的搭配方式，往往視情況而改變其屬性，各種不同的搭配方式至少有五種以上。目前所見的《日書》六畜良忌日有許多混亂難解之處，不過還是可以初步整理出一些選擇原則出來，並用之以復原殘泐漫漶的竹簡。整體而言，雖然還有許多無法理解的部分，但《日書》之六畜良忌日並非全然毫無道理的隨機出現，其數術原理還有待人們重新挖掘與探索。

This article begins by discussing how the Six Domestic Animals are connected with the Five Elements in the extant traditional texts. It then analyzes what the auspicious and taboo days associated with the Six Domestic Animals listed in the Rishu 日書reveal about the qualities of the Five Elements and the principles by which they were selected. According to these traditional texts, the relationships between the Six Domestic Animals and the Five Elements are not fixed: the elements associated with the animals can change depending on the circumstances. Despite the fact that a number of areas of the extant text relating to these auspicious and taboo days are indecipherable, some selection principles can still be ascertained that allow us to infer the content of the partially damaged bamboo slips. Viewed as a whole, the auspicious and taboo days of the Six Domestic Animals in the Rishu do not appear at random, and there is still much to explore and discover about their original divination principles.