A carbon dioxide (CO2) separation membrane plant abnormality detection system includes: an entrance unit through which gas containing CO2 enters a plant including a CO2 separation membrane module; a separation membrane module; a permeation unit configured to discharge the gas with the relatively high CO2 concentration, which is discharged from the separation membrane module, to the outside of the plant; a residue unit configured to discharge the gas with the relatively low CO2 concentration, which is discharged from the separation membrane module, to the outside of the plant; a measurer configured to measure information; and a controller configured to determine the presence of an abnormality, wherein the controller determines whether the plant is in an abnormal situation.