hold (something) over (someone):to use your knowledge of (something) to influence or control the behavior of (someone)(利用掌握的信息)对他人实施影响或控制
She knows about his criminal past and has been holding it over him [=she has been threatening to tell other people about his criminal past] to force him to cooperate.她知道他有犯罪前科并一直以此相要挟,迫使他合作。