The invention provides a temporary plugging agent for horizontal well water control, and a preparation method and application thereof. The temporary plugging agent for horizontal well water control comprises the following raw materials in parts by weight: 4-15 parts of acrylamide, 0.5-3 parts of polypropylene fiber, 1.5-4 parts of reinforcer, 0.5-1.0 part of composite crosslinking agent, 0.1-0.2 part of initiator and the balance of water, totaling 100 parts. The composite crosslinking agent is a mixture composed of polyethyleneglycol diacrylate and N,N-methylene-bis acrylamide in a mass ratio of 10:(1-4). The preparation method of the temporary plugging agent comprises the following steps: sequentially adding the acrylamide, polypropylene fiber, reinforcer and composite crosslinking agent into water, stirring uniformly, adding the initiator, and standing to react for 1-3 hours, thereby obtaining the temporary plugging agent. The invention also provides application of the temporary plugging agent in horizontal well water control. The temporary plugging agent provided by the invention has the characteristics of high gelling viscosity, controllable degradation time, thorough degradation and the like, can plug the high-permeability zone and implement adjustable degradation time, and can lower the damage to the reservoir.