Orocrambus simplex is a moth in the Crambidae family. It was described by Butler in 1877. It is found in New Zealand, where it has been recorded from Westland, Nelson Province, the central part of the North Island and the coastal area of southern Hawkes Bay. The habitat consists of tussock grasslands. The wingspan is 25–33 mm. Adults have been recorded on wing from November to February. Larvae have been reared from Chionochloa rubra, Poa caespitosa and Poa annua.