The traditional paradigm of testing for weak form of Efficient Market Hypothesis (EMH) has a theo- retical obstruction,so in this paper we suggested a new approach to test EMH by testing the conditional pre- dictability of the bit serial that is converted from the original time serial,and defined conditional entropy as the measure of market efficiency.The new approach is simple,clear and advantageous to traditional paradigm for the possibility to quantitatively measure market efficiency.We empir...