The invention relates to an engine room cover of an ultra-large type wind driven generator. The engine room cover comprises an engine room cover body; the engine room cover body is formed by connecting a left cover body and a right cover body which are symmetrical; a connecting part between the left cover body and the right cover body is fixed through bolts; the left cover body and the right cover body are respectively formed by connecting four or six sub-cover bodies; the connecting parts of the sub-cover bodies are fixed through the bolts; skeletons arranged on the sub-cover bodies are connected through the bolts at the end surfaces of flanges; the engine room cover body and an engine room of the wind driven generator are fixed through connection landing legs arranged on the engine room cover body; and a sealant is smeared on joints between the left cover body and the right cover body and joints between every two sub-cover bodies for sealing the cover body. The engine room cover provided by the invention has the advantages that the engine room cover is more reasonable in structural design, convenient and fast to maintain, greatly improves the efficiency of replacing spare parts of a machine set and simultaneously solves the transportation difficult problem caused by the large-scale machine room cover, and the reasonable installment and connection mode of the sub-cover bodies also ensure the integral strength of the machine room cover.