A problem of reversal distance on star-tree is discussed. The problem of 3SAT is induced to the problem of the reversal distance on star-tree with object partially fixed. The fact desribed below is proved, it is still NP-hard to solve the problem of reversal distance on star-tree in which only need to decide the signs of the other symbols to minimizing the sum of distance between object and the given sequences. A polynomial approximation algorithm for the problem is given.