The present disclosure discloses a composite crossarm and a power transmission tower. The composite crossarm includes a post insulator and three suspension insulators. The post insulator and the suspension insulators each has an end configured to be connected to a tower body of the power transmission tower, and another end connected together to form an end of the composite crossarm that is configured to attach a transmission line. The three suspension insulators are arranged at intervals around the post insulator. Axes of two suspension insulators and an axis of the post insulator are in the same plane. The two suspension insulators whose axes are in the same plane as the axis of the post insulator are defined as first suspension insulators, the remaining suspension insulator is defined as a second suspension insulator. The two first suspension insulators form an angle ranged from 45° to 90°.