股票投資研究有很多種方法，許多國內投資人關注特定指標，其中外資買賣超比率
也是投資人主要參考指標之一。過去網路資訊較不流通，造成資訊不對稱，外國機構投資人因資金龐大，因此股市也容易波動受之影響，但現在資訊快速流通下，是否外資能佔有投資優勢，是主要研究內容。本研究以台灣證交所公佈的台灣50指數成份股中的48檔個股為研究對象，樣本期間為2013年11月1日起至2018年10月31日。本文藉由向量自我迴歸模型(VAR)，實證研究觀察二變數外資買賣超比率與個股報酬率探討之間的關聯性。由實證結果得知，一共具有39家個股股價報酬率與外資買賣超比率有正向影響，而其中達到顯著的家數有16家，比例相當高，表示前一日外資買超後，當日股價就上漲；或是前一日外資賣超後，當日股價就下跌，該個股的股價趨勢跟著外資買賣操作而起落，外資明顯佔有股市優勢。
本研究結論如下：
1. 外資買賣超對台灣50指數成份股股價報酬率有顯著影響。顯示外資在台灣股票
市場之大型個股中扮演著領先的角色，可能因為外資對於資訊的判斷以及收集
較精準且資源充足。
2. 外資投資決策有連續性，可能連續投資同方向不只一日，該資訊可作為投資參
考。

There are many methods for stock investment research, and many investors pay attention to specific indicators. Among them, the foreign investor net buy/sell imbalance is one of the main reference indicators for investors. In the past, the Internet information was less circulated resulting in information asymmetry. So the huge amount of foreign investor, that Taiwan's stocks were also affected. However, the information is quickly to circulate than past, whether foreign investors are still has an advantage is the main research content. This study takes 48 stocks of Taiwan 50 index (TW50) constituent stocks as research samples. The research data is from November 1, 2013 to October 31, 2018. This study uses the Vector Autoregression (VAR) model to observe the relationship between foreign investor net buy/sell imbalance and Taiwan 50 Index (TW50) constituent stocks return. The empirical evidence reveals that are 39 companies have a positive impact on foreign investment, and 16 companies of them are significant positively. The proportion is quite high. The stock price trend of the stock followed the foreign trading operation. The foreign investment has market advantage on Taiwan 50 Index. The conclusions of this study are as follows：
1.The foreign investor net Buying/Selling and Taiwan 50 Index (TW50) constituent stocks return have obvious influence. The foreign investors in Taiwan is a leading role in large stocks in the Taiwan stock market, probably because foreign investment in information is judged and collected more accurately and adequately.

2.There is continuity in foreign investment decision-making, and it is possible to invest continuously for more than three days in the same direction that information can be used as reference indicators for home investment.

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