The Simien Mountain Massif is one of the major highlands of Africa, rising to the highest point in Ethiopia, Ras Dejen (4620m), which is the fourth highest peak in the continent. Although in Africa and not too far from the equator, snow and ice appear on the highest points and night temperatures often fall below zero.

The national park has three general botanical regions. The lower slopes have been cultivated and grazed, while the alpine regions (up to 3600m) were forested, although much has now disappeared. The higher lands are mountain grasslands with fescue grasses as well as heathers, splendid Red Hot Pokers and Giant Lobelia.

The park was created primarily to protect the indigenous Walia Ibex, a type of wild goat. Also in the park are families of the Gelada Baboon and the rare Ethiopian wolf. There are more than 50 species of birds have been reported in the Simien mountains.