The present invention relates to a system for detecting ambiguities in a satellite signal for the GPS tracking of vessels, which includes: a GNSS receiving unit obtaining a vessel position using a plurality of satellites; a vessel position calculating unit calculating a second vessel position from a first vessel position after a specific amount of time elapses using dead-reckoning; a distance calculating unit calculating prediction distances between each of the satellites and the vessel and an error monitoring unit comparing the calculated prediction distances between the satellites and the vessel, and pseudoranges between the satellites and the GNSS receiving unit at the second vessel position, and monitoring for the occurrence of errors at the satellites on the basis of the existence of an increase in errors at each of the satellites.