An exhaust gas aftertreatment system for a diesel engine, the exhaust gas aftertreatment system comprising: a treatment agent tank for storing an exhaust gas treatment agent; a metering injection module for injecting exhaust gas treatment agent and metering the injected exhaust gas treatment agent, with the injection of the metering injection module being operated at a predetermined operating frequency and controlled with a determined duty ratio signal according to a desired injection amount; a supply module connected between the treatment agent tank and the metering injection module for supplying the exhaust gas treatment agent to the metering injection module; an exhaust gas treatment agent pipe connected between the metering injection module and the supply module; a pressure sensor for measuring a system pressure in the exhaust gas treatment agent pipe; and a controller configured to: receive a system pressure signal from the pressure sensor during injection of the metering injection module, and detect an injection abnormality of the metering injection module based on at least a first amount, which represents an actual injection amount and is determined by the system pressure signal, and a second amount, which represents a theoretical injection amount and is determined by a corresponding duty ratio signal, characterized in that the controller is further configured to: determine an actual fluctuation amplitude of the system pressure at the predetermined operating frequency of the metering injection module as the first amount by means of frequency analysis of a system pressure signal, and determine a theoretical fluctuation amplitude of the system pressure at the predetermined operating frequency as the second amount from a predetermined relation between an average value of the duty ratio signal and the theoretical amplitude of the predetermined operating frequency. a treatment agent tank for storing an exhaust gas treatment agent; a metering injection module for injecting exhaust gas treatment agent and metering the injected exhaust gas treatment agent, with the injection of the metering injection module being operated at a predetermined operating frequency and controlled with a determined duty ratio signal according to a desired injection amount; a supply module connected between the treatment agent tank and the metering injection module for supplying the exhaust gas treatment agent to the metering injection module; an exhaust gas treatment agent pipe connected between the metering injection module and the supply module; a pressure sensor for measuring a system pressure in the exhaust gas treatment agent pipe; and a controller configured to: receive a system pressure signal from the pressure sensor during injection of the metering injection module, and detect an injection abnormality of the metering injection module based on at least a first amount, which represents an actual injection amount and is determined by the system pressure signal, and a second amount, which represents a theoretical injection amount and is determined by a corresponding duty ratio signal, receive a system pressure signal from the pressure sensor during injection of the metering injection module, and detect an injection abnormality of the metering injection module based on at least a first amount, which represents an actual injection amount and is determined by the system pressure signal, and a second amount, which represents a theoretical injection amount and is determined by a corresponding duty ratio signal, characterized in that the controller is further configured to: determine an actual fluctuation amplitude of the system pressure at the predetermined operating frequency of the metering injection module as the first amount by means of frequency analysis of a system pressure signal, and determine a theoretical fluctuation amplitude of the system pressure at the predetermined operating frequency as the second amount from a predetermined relation between an average value of the duty ratio signal and the theoretical amplitude of the predetermined operating frequency. determine an actual fluctuation amplitude of the system pressure at the predetermined operating frequency of the metering injection module as the first amount by means of frequency analysis of a system pressure signal, and determine a theoretical fluctuation amplitude of the system pressure at the predetermined operating frequency as the second amount from a predetermined relation between an average value of the duty ratio signal and the theoretical amplitude of the predetermined operating frequency.