A method for estimating a target range error in an active sonar system, the method comprising: a) setting a search range boundary (R s) of a target for range error estimation, under initial conditions of a 1-way target detection time (T sonar) and a detected range of a target (R sonar) detected by an active sonar, wherein the detected range (R sonar) of a target is calculated by multiplying the 1-way target detection time (T sonar) with a sound velocity; b) inputting environmental data of an area where the target is located, wherein the environmental data comprises depths and an underwater sound velocity structure; c) predicting a multipath eigenray time (T path (i,j,k)) and a multipath eigenray pressure (P path (i,j,k)) at each multipath (k), range (j) and depth (i) within the search range boundary (R s), by detecting multipath eigenrays reflected from the target; d) filtering the detected multipath eigenrays so as to extract a time(T path (i,j)) of a dominant pressure path or a first arrival path among the predicted multipath eigenrays; e) searching, at each depth, a horizontal range (R(i)) that the filtered dominant or first arrival path time (T path (i,j)) matches the detected 1-way target detection time (T sonar); and f) estimating a target range error (R error (i)) between the searched horizontal range (R(i)) corresponding to a matching time (Tp ath (i)), and the detected range of a target (R sonar) calculated based on the detected 1-way target detection time (T sonar), wherein the target range error R error (i) is estimated through the following equation, R error (i)=R(i)-R sonar, where the R(i) indicates the searched horizontal range corresponding to the matching time (T path (i)), and the R sonar indicates the detected range of a target calculated based on the detected 1-way target detection time (T sonar). a) setting a search range boundary (R s) of a target for range error estimation, under initial conditions of a 1-way target detection time (T sonar) and a detected range of a target (R sonar) detected by an active sonar, wherein the detected range (R sonar) of a target is calculated by multiplying the 1-way target detection time (T sonar) with a sound velocity; b) inputting environmental data of an area where the target is located, wherein the environmental data comprises depths and an underwater sound velocity structure; c) predicting a multipath eigenray time (T path (i,j,k)) and a multipath eigenray pressure (P path (i,j,k)) at each multipath (k), range (j) and depth (i) within the search range boundary (R s), by detecting multipath eigenrays reflected from the target; d) filtering the detected multipath eigenrays so as to extract a time(T path (i,j)) of a dominant pressure path or a first arrival path among the predicted multipath eigenrays; e) searching, at each depth, a horizontal range (R(i)) that the filtered dominant or first arrival path time (T path (i,j)) matches the detected 1-way target detection time (T sonar); and f) estimating a target range error (R error (i)) between the searched horizontal range (R(i)) corresponding to a matching time (Tp ath (i)), and the detected range of a target (R sonar) calculated based on the detected 1-way target detection time (T sonar), wherein the target range error R error (i) is estimated through the following equation, R error (i)=R(i)-R sonar, where the R(i) indicates the searched horizontal range corresponding to the matching time (T path (i)), and the R sonar indicates the detected range of a target calculated based on the detected 1-way target detection time (T sonar).