Both the Taiwanese and Japanese government adopted the relevant banned short selling under the financial tsunami. This paper analyzes the short-selling constraints from the theoretic and practical perspectives and performs an empirical study on the policy effectiveness of complete short-selling bans Both Taiwan and Japan. This paper finds that the constraints on short selling affect trading volumes, and enhance the fluctuations of the market. As a result, the market mechanism cannot operate normally. Although the policy of suppressing market declines sees results in a short period of time, the policy loses its meaning over the long term. It is the consistent result with scholars that the government should not adopt any measures to intervene in the market mechanism. In fact, the government should do good reform beneficial to market operations.