Abstract The detection of randomly distributed extended multi-targets under various circumstances is of special interest. An improved plot fusion method is proposed in this work. The proposed plot fusion method is based on a multi-contour tracking and region growing algorithm. The proposed method is applied to the DP-TBD algorithm for extended targets in the K-distributed sea clutter. Models and shortcomings of existing methods are presented. The principle of the DP-TBD algorithm for extended targets and implementation of the improved plot fusion method are explained in detail. In the simulation, the methods are applied to almost all situations, close trajectories, crossing trajectories, small targets, weak targets and targets in a high clutter region. Comparison with existing methods demonstrates that the proposed method is practical and superior to the existing methods.