The invention discloses a method and system for judging the copying state of a subscriber identification card, which is used for effectively monitoring whether the SIM card of a subscriber is copied or not in real time on the premise of not modifying the core network. The method comprises the following steps: monitoring the call failure incident record corresponding to the international mobile subscriber identification IMSI; and when the call failure reason contained in the call failure incident record is that the IMSI does not register in the visitor location register VLR of the subscriber terminal corresponding to the IMSI, judging whether the subscriber identification card is copied by inquiring whether the subscriber identification card corresponding to the IMSI is in the defaulting state.