The invention relates to a fabricated cable trench and a construction method. The fabricated cable trench comprises side plates, a top plate and a bottom plate. Each side plate comprises a first end and a second end which are oppositely arranged, the first end is provided with a first tenon, and the second end is provided with a second tenon. There are at least two side plates, and the two side plates are oppositely arranged. The two ends of the top plate are connected to the two oppositely-arranged side plates, and the end of the top plate is engaged with the first tenon. The two ends of thebottom plate are connected to the two oppositely-arranged side plates, and the end of the bottom plate is engaged with the second tenon. By using the fabricated cable trench of the invention, damagesto an original cable trench in a construction process are effectively prevented, normal operation of the original cable trench is ensured, construction steps are simple and easy, and construction efficiency is increased. In addition, according to the fabricated cable trench, step-by-step construction is performed, the side plates are constructed firstly, then the top plate is constructed, and finally the bottom plate is constructed. The construction steps are simple and easy to implement, and construction difficulty is low.