Beside the influence of information flow on stock price volatility, to study whether disposition effect, a kind of investor's different decision-making behavior, also has some important influence on stock price volatility, this paper introduces capital gains overhang to GARCH-V model and establishes GARCH-V-G Model, chooses stock index on developed market and emerging market respectively as samples and makes a comparative empirical study. The results show the capital gains overhang is negatively related to price fluctuation on stock markets, which means investors with capital gains weaken the price volatility while with capital losses intensify the volatility. Moreover, the capital gains overhang can explain to some extent the persistence of stock price volatility, and the disposition effect shown by investors on emerging markets can explain better and affect greater the continual volatility than that on developed markets.