本文探討中國大陸農村地區出生性別比明顯偏高的原因。我們認為，現行的人口政策與社會環境因素衍生之男孩偏好的交織是問題的根源。本文提出了一個分析中國大陸農村出生性別比失衡的分析框架，並且由農戶生育選擇的角度，論證在發展相對落後的中國大陸農村，由於農戶缺乏可與「嬰兒」相競爭或可替代的資本財，而「女兒」在農業生產、養老、財產繼承等方面又處於相對劣勢。在強制性人口政策對嬰兒數量的限制下，於「邊際上」，相對於「女兒」，「兒子」帶給父母的價值或效用迅速提高，這是大陸農村地區出生性別異常偏高的主要原因。適當的政策調整，改善農村地區社會經濟條件並促進農戶所得的提高是緩解中國大陸農村地區出生性別比失衡問題之關鍵。

The purpose of the paper attempts to shed light on the main reason why the sex ratio at birth in rural China is obvious high compared with urban and other societies. We argue the one-child policy introduced by P. R. C. government and traditional Chinese culture have most important effects on the salient fact about the sex ratio at birth since 1980s. We set up a conceptual framework and a relevant theoretic model to explain the rationale that the parents display son preference under the severe population policy in terms of marginal calculation. The key points of improving the high sex ratio at birth are the deregulation and the upgrading local economic conditions in rural regions.