Stocks are highly traded assets in capital markets and have become increasingly popular as financial literacy has risen. However, investing in stocks necessitates a balanced understanding and expertise due to their potential for high returns coupled with high risks. This research examines the stability and predictive ability of two prominent portfolio models—the Markowitz Model and Index Model—in the context of the Chinese stock market during the COVID-19 pandemic, while considering 4 distinct constraints. Criteria such as ROA, Sharpe ratio, and risk diversification are pivotal in stock selection. The Markowitz Model emphasizes diversification and risk management strategies, aiming to minimize overall portfolio risk. In contrast, the Index Model explores the correlation between individual security returns and market movements, focusing on capturing broader market trends. By analyzing data spanning from 2007 to 2022, this study sheds light on which model performs more effectively in navigating challenging market conditions, providing valuable insights and guidance for investors amidst uncertainty.