Abstract: An easy assembly outdoor sofa is disclosed, comprising such components of a base and a backrest (or armrest). The plane of the base extends horizontally to form a seat, and the periphery of the base is formed with a bar portion having oval section. The bar portion extends downward to form a frame, wherein the bottom of the backrest (or armrest) extends laterally to form an L-shaped connecting portion. A C-shaped opening is formed at the intersection part between the bottom and the L-shaped connecting portion. The C-shaped opening is to receive the oval bar portion of the base; as a characteristic feature, both the upper edge and lower edge of the bar portion of the base are configured with a positioning tenon, and corresponding to the positioning tenon, the L-shaped connecting portion is configured with a positioning mortise with larger width. Moreover, the base and the L-shaped connecting portion are configured with fixing holes matching each other.