The invention provides a float collar device preventing floating of a rubber plug and a well cementation method; the float collar device comprises a coupling and a float collar shell; the lower end of the coupling is connected with the float collar shell, a valve seat, a coated valve and a spring seat are arranged in the float collar shell, the valve seat is fixed in the float collar shell, the spring seat is connected to the lower portion of the valve seat, the coated valve may axially move along the coated valve, the coupling includes a floating preventive portion arranged at the upper portion of the coupling, and the inner diameter of the floating preventive portion is less than the outer diameter of the rubber plug and the inner diameter of the upper and lower portions of the rubber plug. By adding a centralizing structure, a floating preventive structure and a bumping ring structure, the float collar device is imparted the functions of rubber plug centralizing, rubber plug floating prevention, significant bumping for the rubber plug, and reverse effective cutoff; the float collar device is applicable to oil-gas horizontal wells having a complex depth structure and a long horizontal segment.