台股屬於淺碟型市場，每當國內外金融環境發生重大事故，導致資本市場、金融市場與股市大幅修正時，此時隸屬於行政院的國家金融安全基金 (簡稱國安基金)，就肩負起穩定股市的重責大任。本研究主要在探討國安基金進場護盤的時間點是否與文獻上常用來認定牛、熊市的轉折時點相符合。若實證結果發現護盤進場時點與牛、熊市判斷時間相吻合，表示國安基金進場護盤的交易策略值得投資人參考。我們分析的資料從 2008 年第四次國安基金護盤到 2020 年第七次國安基金護盤 (共四次護盤)。研究發現，除了第六次 (人民幣為主的亞洲匯率重挫引發金融危機) 與第七次 (新冠肺炎全球大流行) 國安基金的進場點符合熊市轉牛市的轉折點進場，其餘兩次 (第四次因美國次貸危機引發的全金融海嘯事件與第五次因希臘債信問題引發的歐債危機) 進場時間皆不符合牛、熊市轉折點。因此國安基金的進出場點與交易策略仍有改善的空間。在此情況下，我們嘗試運用過往經驗找到較佳的交易策略，運用國安基金進場護盤的特性 (國安基金護盤時，購買的標的多半是跌深且權值較重的電子與金融類股)，購買國安基金護盤前跌幅較大的類股，待國安基金宣布離場後賣出，獲得較佳的投資報酬，透過實證結果發現，我們的交易策略確實可以提高交易勝率。

Taiwan's stock market belongs to the shallow type. When major domestic or international events lead to significant corrections in the capital, financial and stock markets, the National Financial Stabilization Fund (referred to as the "Fund"), which is under the jurisdiction of the Executive Yuan, is given the responsibility of stabilizing the stock market. This study aimed to investigate whether the time points at which the Fund intervenes to protect the market are consistent with the turning points commonly used in the literature to identify bull and bear markets. If the empirical results show the time points of intervention are in line with the turning points that are used to determine bull and markets, the trading strategy of the Fund is worthy of reference for investors. We analyzed the data from the fourth intervention in 2008 to the seventh intervention in 2020 (total of four interventions). The study found that only the time points of the sixth intervention (for the financial crisis triggered by crash of Chinese Yuan and other Asian currencies) and the seventh intervention (for the outbreak of COVID-19) match the turning points from bull to bear market. The other two interventions (the fourth for the subprime mortgage crisis in the United States and the fifth for the European debt crisis due to the failing credits of Greece) are not in line with the turning points of bull and bear market. Therefore, there is still room for improvement in time points of the Fund's intervention and its trading strategies. Given the results, we tried to apply previous experiences to identify a better trading strategy. Considering the characteristics of the Fund's intervention strategy (most of the targets of intervention are heavyweight electronic and financial stocks with deep decline), better investment returns were obtained through buying stocks with significant decline before intervention and selling them after intervention. Empirical results show our trading strategy can indeed improve the investment return.

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