Disclosed are a method for measuring a acoustic transfer function of a predetermined space to be secured or monitored through a correlation between sound signals acquired from a sound source generating device and a sound measuring device and a method and a system for judging whether there is an intrusion object by using a difference between an initially set acoustic transfer function information and varied acoustic transfer function information by using the method for measuring the transfer function. In the present disclosure, when an object moves or an intrusion object is generated in a predetermined space, intrusion or no intrusion is monitored by variation of the acoustic transfer function varied by the intrusion object even though there is no noise generated by the intrusion object.