自己也不wiki一下...下面几段话能回答你全部问题.
In the United States, the IRS defines the ex-dividend date as "the first
date following the declaration of a dividend on which the buyer of a stock
is not entitled to receive the next dividend payment."
The ex-dividend date is two business days prior to the record date. To be a
stockholder on the record date an investor must purchase the stock before
the ex-dividend date. The latest date he can buy the stock to be a
stockholder on record and be entitled to the dividend would be one day prior
to the ex-dividend date to allow for the three stock trading day settlement
of the stock purchase. If the investor purchases the stock the day before
the ex-dividend date the investor would be a stockholder on the record date
and would be entitled to receive the dividend payment.[6]
An investor who wishes to be entitled to the dividend does not have to wait
until after the record date to sell the stock; however, the investor must
hold the stock until the ex-dividend date. If the investor were to sell the
stock on the ex-dividend date or afterwards, the investor would still be
entitled to the dividend payment. In this example, assuming that the
investor purchased the stock one day before the ex-dividend date, the
investor would be a stockholder on the record date. If the investor sells
the stock on the ex-dividend date, the buyer of the stock would be a
stockholder one day after the record date given the three stock business
trading day settlement. The person that bought the stock would not be
entitled to receive the dividend.[citation needed]
An investor only needs to own the stock for one day (the record date) to be
entitled to receive the dividend payment. If the investor buys before the ex
-dividend date, and sells on the ex-dividend date or after, the investor
will receive the dividend payment.
