The invention discloses a synchronous sliding mechanism, a side hidden door system, and a cabinet body with the side hidden door system. The synchronous sliding mechanism comprises a guide rail and a first connecting rod mechanism, wherein the first connecting rod mechanism comprises two sliding ends provided on the guide rail; and when the guide rail reciprocates in a horizontal axial direction, the two sliding ends are close to or far away from each other. Through connection between connecting rods and the guide rail, the guide rail may reciprocate stably and synchronously. The synchronous sliding mechanism is widely suitable for furniture such as door bodies, cabinet bodies and the like, and has an excellent effect.