An adaptive equalizer, comprising: a filter, configured to filter input signals according to a first filter coefficient to obtain a first filter signal, and further configured to filter the input signals according to a second filter coefficient to obtain a second filter signal; a coefficient updating unit, configured to buffer the input signals to obtain buffer signals, and further configured to obtain an update magnitude of the filter coefficient according to a level n - 1 error signal and the buffer signals, and obtain the second filter coefficient according to the update magnitude, wherein n is a positive integer greater than 1; a standard decider, configured to decide the first filter signal based on an original constellation map to obtain a first decision signal, and further configured to decide the second filter signal based on the original constellation map to obtain a second decision signal; a level decider, configured to decide the first filter signal based on a level n - 1 constellation map to obtain a level n -1 pseudo decision signal, and further configured to switch the level n - 1 constellation map to a level n constellation map if average energy of the level n - 1 error signal is smaller than a level n - 1 threshold, wherein the level n constellation map is the original constellation map; and a comparator, configured to compare the level n - 1 pseudo decision signal with the first filter signal to obtain the level n - 1 error signal; characterized in that the level decider comprises a constellation map obtaining module, the constellation map obtaining module is configured to: in four quadrants of a coordinate system, group all constellation points in the level n constellation map into regular areas, where the regular areas satisfy two conditions: the regular areas are contiguous, and one regular area cannot be blocked by another; and the number of covered original constellation points in regular areas at the same level is the same, and the relative positions of the original constellation points in the regular areas are the same; and further configured to use the centroid point of each regular area as a new constellation point and use the perpendicular bisector of each centroid point as a decision partition line for the new constellation points, to obtain the level n - 1 constellation map. a filter, configured to filter input signals according to a first filter coefficient to obtain a first filter signal, and further configured to filter the input signals according to a second filter coefficient to obtain a second filter signal; a coefficient updating unit, configured to buffer the input signals to obtain buffer signals, and further configured to obtain an update magnitude of the filter coefficient according to a level n - 1 error signal and the buffer signals, and obtain the second filter coefficient according to the update magnitude, wherein n is a positive integer greater than 1; a standard decider, configured to decide the first filter signal based on an original constellation map to obtain a first decision signal, and further configured to decide the second filter signal based on the original constellation map to obtain a second decision signal; a level decider, configured to decide the first filter signal based on a level n - 1 constellation map to obtain a level n -1 pseudo decision signal, and further configured to switch the level n - 1 constellation map to a level n constellation map if average energy of the level n - 1 error signal is smaller than a level n - 1 threshold, wherein the level n constellation map is the original constellation map; and a comparator, configured to compare the level n - 1 pseudo decision signal with the first filter signal to obtain the level n - 1 error signal; characterized in that the level decider comprises a constellation map obtaining module, the constellation map obtaining module is configured to: in four quadrants of a coordinate system, group all constellation points in the level n constellation map into regular areas, where the regular areas satisfy two conditions: the regular areas are contiguous, and one regular area cannot be blocked by another; and the number of covered original constellation points in regular areas at the same level is the same, and the relative positions of the original constellation points in the regular areas are the same; and further configured to use the centroid point of each regular area as a new constellation point and use the perpendicular bisector of each centroid point as a decision partition line for the new constellation points, to obtain the level n - 1 constellation map.