A special relation of sidebyside triangles forms between the target tracks and the radars in the air or on the sea. In the view of these special triangles, the paper introduces some definitions of sidebyside triangles on a plane or a sphere, and investigates their geometric theorems and algebraic constraints. Aimed at the problems that target states change and the measurement information exists in shortages, the paper respectively uses the relation between sides and angles of a triangle and the traditional method to design the simulation. The simulation result shows that because of motion model mismatch or big measurement interval, the traditional method has many errors, while the method used by relation between sides and angles of sidebyside triangle draws a better result, and the adaptation and the effectiveness of sidebyside triangle in actual combat are tested and verified.