In addressing the persistent challenge of rheological control in high-temperature and high-density water-based drilling fluids（WBDFs），a new high-temperature zwitterionic polymer viscosity reducer（HP-THIN）was prepared based on molecular structure optimization design and monomer optimization using orthogonal experiments and single-factor experiments. The molecular structure，thermal stability and relative molecular weight of HP-THIN were characterized and determined by infrared spectroscopy，Ulrich viscometer，and thermogravimetric analysis. The viscosity-reducing ability of HP-THIN on different types of drilling muds such as freshwater mud，salt-containing mud，calcium-containing mud，and high-density composite salt-containing mud was investigated at the temperature of 220 ℃. The effects of HP-THIN on adsorption capacity，zeta potential，and particle size of base-mud clay were tested at ambient temperature and compared with similar commercial viscosity reducers Polythin and xy-27. The results showed that，the optimal reaction recipe of the HP-THIN was as follows，the reaction temperature was 60 ℃ ，thereaction time was 3 h，the amount of initiator and chain transfer agent was 1%（based on the total amount of monomers），and the total mass fraction of the monomer was 30% and the molar ratio of AM，AA，AMPS and PTM was 1.9∶7.5∶2.1∶1. The viscosity-average relative molecular weight of the obtained HP-THIN was about 8211，and the HP-THIN exhibited good thermal stability. After aging at the temperature of 220 ℃ ，the viscosity reduction rates of HP-THIN at the optimal dosage of 0.3% on freshwater-based mud，salt-water-based mud，calcium-containing base mud，and high-density composite salt-water-based mud reached 86%，72%，73%，51%，respectively. Compared to xy-27 and Polythin，HP-THIN demonstrated better high-temperature viscosity reduction effect in all different types of drilling fluid base mud due to its strong adsorption capacity with clay platelets， large absolute value of zeta potential，which was conducive to unentangling the complex polymer network structure between clay particles，significantly decreasing the viscosity of the drilling fluid，showing good application prospects.