We investigate a practical semi-autonomous power distribution line maintenance robot system which performs jobs using task level directions. We are developing a CG (computer graphics) simulator for investigation of the conceptual design of our proposed robot system. This robot system has a vehicle, a boom, an approach arm, and left and right work arms. We teach the motions through a series of move commands for a task, and these commands are stored in a task knowledge database. The taught positions of the motions are expressed as task object coordinates. This paper describes the architecture and the performance of the CG simulator system, and provides an example of maintenance tasks. In simulations, we show that the task can be performed in different work environments using the same commands taught in the task object coordinate system for the sequence task, "install the switch gear"