The invention discloses a well cementing slurry large temperature difference retarder and its preparation method, and relates to a field of casing and cementing of exploration and development of oil and gas. The large temperature difference retarder mainly comprises three structure units which are anion monomer 2- acrylamide-2- methyl propanesulfonic acid (AMPS), cationic monomer methylacryloyl yloxyethyl trimethyl ammonium chloride (DMC) and nonionic monomer acrylamide (AM); the mass by part of every component is: AMPS is 60-70 parts, DMC is 20-25 parts and AM is 10-15 parts. The large temperature difference retarder is prepared by an inverse emulsion polymerization method; the inverse emulsion fluid is prepared from, by mass, 60-65 parts of white oil, 35-40 parts of deionized water, 6.0-6.4 parts of Span 80, 0.6-1.0 part of Tween 80. The retarder can realize the retarding function of cement slurry in the whole temperature zone where the upper and lower ends of the cement injection well section for well cementing construction are 50 and 150 DEG C; the comprehensive performance of the cement slurry system can meet the requirement of the well cementing construction of a thermal production well.