An optical fiber connector assembly and a connecting system are disclosed. The optical fiber connector assembly includes a first accommodating groove and a second accommodating groove concavely provided in sequence backward from a front end surface of the sliding seat and intercommunicated with each other. A width of the second accommodating groove is less than a width of the first accommodating groove. A step surface is provided between the first accommodating groove and the second accommodating groove. An optical fiber connector is mounted on the sliding seat and floatable with respect to the fixing seat along a front-rear direction, a left-right direction and a vertical direction. A mating section of the optical fiber connector is located in the first accommodating groove. A connecting section is partially accommodated in the second accommodating groove. The step surface is located behind the mating section to stop the mating section from moving backward.