Molecular motors are the frontier topic in biology and physics,and the dynamic mechanism of directed transport attracts much attention.In most cases,molecular motors operate in groups.The interaction and cooperation among motors play an important role in the collective behaviors of molecular motors.The behaviors and mechanism of collective transport of molecular motors are sketched out.Furthermore,two cases are detailedly discussed in which the cooperation among motors is needed for the implementation of directed transport.In the first case,the cooperation impels directed motion under overdamping condition.In the second case,through cooperation molecular motors can gain energy from driving in one direction and do work in the vertical direction,and then cause transversal drift.