本省由於工業快速發展，而農業發展較落後的緣故，造成鄉村農業地區的人口大規模地移往都市工業中心。這種水平的移動引起多方面的改變，其中最廣泛被提到的，即農場勞力的短缺。因此集約勞力經營無法像以往般地，受到鼓勵。 本研究的主要目的在探討台灣農業人口外移與複種作物制度之關係。文中首先指出本省農業人口外移趨勢：此一部份論及農業人口、農業勞力的外移量與外移率。第二部份說明遷移型態和作物指數之關係；本部份分三方面討論：(1)二次大戰役初期，農業人口較少外流且較穩定，尚未造成複種指數的下降；至一九六六年後，外移率開始促使複種指數下降。(2)觀察不同區域農業人口外移與複種指數的關係。複種指數較低地區具有吸收其他地區農業勞力之能力；反之，複種指數較高地區，農業勞力顯現外移情形。這種現象發生在工業化之前時期，但在高度工業化和都市化時期，此現象却變得本規則。 (3)在農家層次上，比較遷移型態和複種指數關係。通勤的遷移者，這種遷移型態和高的複種指數有關，亦即此種遷移者比其他遷移者(永久性遷移者及季節性遷移者)貢獻更多的勞力在農業經營上，或者可以說高複種指數作物經營的農家比其他農家需要更多家中遷移分子的部分勞力。另外在第三、四、五節分別討論遷移者的特性和職業的獲得，遷移者在複種作物經營上扮演的角色和貢獻，及遷移率與複種指數的趨勢。

With rapid industrial developments and lagging agricultural developments in Taiwan, rural populations are migrating to urban and industrial centers in a large scale. These horizontal movements are creating changes in multiple aspects, in which agricultural labor shortage is a common issue. Therefore, labor-intensive operations can no longer be encouraged as before. This study aims to discuss the relationship between agricultural emigration and multiple-crop farming in Taiwan. First, we point to agricultural emigration trends in Taiwan. This section touches upon agricultural population, as well as emigration quantity and ratio in agricultural labor. The second section describes the relationship between emigration pattern and crop index, which is further divided into three aspects. 1. After Second World War, agricultural population was stable with little emigration. After 1966, higher emigration led to falling multiple-crop index. 2. Observe the relationship between agricultural emigration and multiple-crop index in different regions. Regions with lower multiple-crop index are capable of attracting agricultural labors from other regions. On the other hand, agricultural emigration is more prominent in regions with higher multiple-crop index. This pattern happened before industrialization. However, with advanced industrialization and urbanization, this pattern becomes irregular. 3. Compare relationships between different emigration patterns and multiple-crop index in farming families. Commuting migrants are correlated to high multiple-crop index. These migrants contribute more labor to agricultural operations than others (permanent and seasonal migrants). In other words, farming families with higher multiple-crop index require more partial labor from migrants in family. The third, fourth, and fifth sections explore migrant attributes and occupations, migrant roles and contributions to multiple-crop farming, and trends in migration ratio and multiple-crop index.