A rocker arm compartment assembly for a heavy-duty diesel engine comprises a rocker arm compartment and a cam bearing cap. The top of the rocker arm compartment is connected with a cylinder head cover. The bottom of the rocker arm compartment is connected with a cylinder head. A first intake camshaft installation groove and a first exhaust camshaft installation groove are symmetrically formed in the rocker arm compartment. The cam bearing cap comprises first cam bearing cap bodies and second cam bearing cap bodies. The top of each first cam bearing cap and the top of each second cam bearing cap are each provided with an intake rocker arm shaft installation arc surface matched with an intake rocker arm shaft and an exhaust rocker arm shaft installation arc surface matched with an exhaust rocker arm shaft. The bottom of each first cam bearing cap and the bottom of each second cam bearing cap are each provided with a second intake camshaft installation groove matched with the first intake camshaft installation groove and a second exhaust camshaft installation groove matched with the first exhaust camshaft installation groove. The rocker arm compartment assembly is applicable to the engine with double overhead camshafts and double rocker arm shafts; besides, part distribution is simplified while step-by-step braking of the engine is achieved.