Embodiments of the present disclosure disclose an IMSI acquisition method and device, and a signaling monitoring system. The IMSI acquisition method provided by the embodiment of the present disclosure includes: collecting an S1-MME interface signaling and a first interface signaling which is associated with the S1-MME interface signaling; acquiring a first identity from the S1-MME interface signaling; acquiring an IMSI and a second identity from the first interface signaling, herein the second identity is an identity which is associated with the first identity; associating the first identity, the second identity and the IMSI; and acquiring the corresponding IMSI according to an association result and the first identity in the S1-MME interface signaling.