Since Arthur's Pass National Park is part of the Main Divide, the eastern and western side have climatic differences and vary in their vegetation accordingly.
Mountain beech (Fuscospora cliffortioides) is prevalent in the drier east. This species adapts to several altitudes and may quickly recover from external damages. Joining it on a few patches are silver beech (Nothofagus menziesii) and red beech (Fuscospora fusca) trees that the mountain beech often hybridises with. Other tree species found here are ribbonwood (genus Plagianthus), marble and broad leaf. Shrubs make up the forest's undergrowth such as manuka (Leptospermum scoparium), koromiko (Veronica salicifolia, stricta) and coprosma (genus Coprosma). Numerous fern species contribute to the bushes as well.
The west contains beech species as well. Due to the heavy annual rainfall however, a dense podocarp rainforest dominates the territory. Species include the kahikatea (Dacrycarpus dacrydiodes), totara (Podocarpus totara), rimu (Dacrydium cupressinum), kamahi (Weinmannia racemosa), marble and broad leaf as well as the southern rata (Metrosideros umbellata) and more. The rainforest has a thick understory made up of shrubs, ferns, herbs and mosses.
Higher altitudes of the park are home to many tussock and shrub lands as well as alpine flower species. Examples are alpine daisies (genus Celmisia), snowberry (Gaultheria antipoda), gentians (genus Gentiana), buttercups (genus Ranunculus), Arthur's Pass forget-me-not (Myosotis explanata) and many more.