Administrative procedure legislation is a weak link in China, but there are administrative actions violating administrative procedure ligislation at times. So it needs to improve the legal liability mechanism in illegal administrative procedure. This paper defines the subject and scope of illegal administrative procedure, and analyzes the present adminastrative procedure legislation rules and liability judgement. Then it suggests that there is deficiency of liability stipulation, nonstandard stipulation of liability, and imperfection of liability forms. In order to perfect the legal liability mechanism in illegal administrative procedure, it needs to complete the legal liability forms, such as invalid, revoked, and revised, in illegal administrative proceduree; and also needs to improve the liability investigation mechanism in illegal administrative procedure, guaranteeing rationality and legitimacy of enforcing administrative rights.