A steering mechanism of an all-terrain vehicle includes: a steering shaft; a power steering system; and an adjusting mechanism including a ball joint, a first connecting shaft and a second connecting shaft. The first connecting shaft has a first end provided with a first ball groove, the second connecting shaft has a first end provided with a second ball groove, and the first ball groove and the second ball groove each accommodate a partial structure of the ball joint, such that the first connecting shaft and the second connecting shaft are rotatably coupled by the ball joint; and a second end of the first connecting shaft away from the first ball groove is coupled to the steering shaft, and a second end of the second connecting shaft away from the second ball groove is coupled to the power steering system. An all-terrain vehicle is also disclosed.