A heavy-duty diesel engine split type rocker arm brake mechanism for a commercial vehicle comprises a rocker arm body, a swing mechanism and a hydraulic drive system; the rocker arm body is mounted on a rocker arm shaft through a main mounting hole, the swing mechanism comprises a swing head, a first adjusting bolt and a rolling column, the swing head is mounted on the rocker arm body, a sheet-shaped spring is arranged at the bottom of the swing head, and is pressed on the bottom of the rocker arm body, a ball head of the first adjusting bolt is mounted in a ball socket in an elephant foot shape, the hydraulic drive system comprises a hydraulic plunger with a return spring sleeved, a second adjusting bolt in contact with the hydraulic plunger and a rocker arm cam in threaded connection with the hydraulic plunger, the hydraulic plunger is mounted in a drive cavity of the rocker arm body, the rocker arm cam makes contact with the rolling column, a brake hydraulic oil way communicated with the main mounting hole, the drive cavity and a swing arm shaft hydraulic oil hole is arranged in the rocker arm body, and the heavy-duty diesel engine split type rocker arm brake mechanism is high in reliability, low in cost, high in lightweight degree, simple in structure, convenient to assemble and maintain and good in brake effect.