The present invention discloses a method for detecting dispersion, overcoming disadvantages of complex configuration and insensitivity to a tiny dispersion of the method and device for detecting dispersion in the prior art. The inventive method includes: obtaining a signal within a predetermined bandwidth range from an optical signal received; obtaining an operated value of power via an operation on the signal within the predetermined bandwidth range; and obtaining amount of system dispersion according to a corresponding relation between the operated value of power and the amount of system dispersion. A device for detecting dispersion is disclosed, including a photoelectric filter operational unit and a processing unit, where an output of the photoelectric filter operational unit is connected to an input of the processing unit. The device for detecting dispersion of the present invention is applicable to an adaptive dispersion compensation system. An optical signal transmission system is further disclosed.