Abstract: An idealized moist baroclinic wave simulation was performed to describe the rapid development of an extratropical cyclone. Warm and cold conveyor belts were then identified using the Lagrangian trajectory selection method, and physical quantities along their trajectories were diagnosed, followed by the analysis of their impacts on the precipitation. The study similarly presents previous conclusions of conveyor belts and finds some more refined structures, especially for cold conveyor belts. Results reveal that warm conveyor belts could generally split into “forward-sloping ascent” and “rearward-sloping ascent” branches. They originate in the warm sector ahead of the cold front and low level and move respectively forward and rearward relative to the cyclone center when they spiral upward to the upper and middle level, generating a negative potential vorticity disturbance upon the outflow region and promoting the development of the upper system. They also transport abundant moisture upward and significantly influence the formation and maintenance of the precipitation extremum around the front. Cold conveyor belts are confirmed to represent two branches of ascent and the remaining in the lower level as described by previous researches, which could then be classified finely into four branches. “Forward-sloping ascent” and “rearward-sloping ascent” branches originate near the warm front and curve separately forward and rearward relative to the cyclone center when rising upon the middle level, benefiting the rainfalls around the warm front. Meanwhile, branches of “wrapping around the cyclone and forward-sloping” and “wrapping around the cyclone and rearward-sloping” always stay in the lower level and move from the east of the surface cyclone far from the warm front toward the cyclone center whenever their vapor content increases. They then respectively descend anticlockwise and clockwise to the downstream and upstream of the cyclone after traveling slowly upward west of the cyclone around the center, inducing the little precipitation northwest of the cyclone.