A B(left-arrow)N bridging thiophene with thiazole-based conjugated polymer and a preparation method and application thereof belong to the technical field of polymer solar cells. The technical problem of low energy conversion efficiency of a polymer solar cell in the prior art is solved. The conjugated polymer has a structure shown in a formula (I). Through the different electron donating abilities and the different bonding angles of copolymerization with an electron withdrawing unit of a bridging unit (Ar2), and the length variation of an alkyl chain, the electronic structure of the conjugated polymer is effectively adjusted, the conjugated polymer is enabled to have the advantages of a narrow band gap, a wide absorption spectrum, low LUMO/HUMO energy level, high electronic mobility and the like. Through detection, the LUMO energy level of the conjugated polymer is between -3.60eV and -4.0eV, the optical band gap is less than 1.8eV, the film absorption spectrum is 300 to 900nm, the electronic mobility is 10<-2> to 10<-5>cm<2>V<-1>s<-1>, and the conjugated polymer can be used as an acceptor material of a high-performance solar cell. The formula (I) is shown in the description.