Abstract: In cementing long openholes, cement retarders sometimes lose their effectiveness because of high temperatures. Slow development of the strength of the top cement slurry, sensitivity of cement slurry to temperature and to the dosage of cement additives are problems encountered during well cementing. To address these problems, a high temperature retarder CXT-1 has been developed with acrylic acid (AA), itaconic acid (IA), 2-acrylamide-2-methylpropane sulfonic acid (AMPS) and a new cationic monomer (X). The optimum synthetic conditions obtained through orthogonal experiment are as follows:molar ratio of the monomers is 37:8:8:6, reaction temperature is 60℃, pH of the reaction solution is 4, time of reaction is 4 h, and the concentration of initiator is 0.3%. CXT-1 was characterized with IR spectroscopy, NMR and thermogravimetric analysis, and evaluated in laboratory. It was found that the molecules of CXT-1 contains the characteristic functional groups of the four monomers. CXT-1 has good thermal stability, and no obvious mass lose of CXT-1 was found when temperature is less than 330℃. Using CXT-1, the thickening time of a cement slurry can be prolonged at temperatures between 90℃ and 180℃. At 180℃, the thickening time is 368 min. The concentration sensitivity coefficient of CXT-1 is in a range of 0.48 - 1.73, and the maximum temperature sensitivity coefficient of CXT-1 is 6.2%, all satisfying the needs of the relevant industrial standards. The 24 h compressive strength of the top cement slurry at temperatures between 60℃ and 100℃ is at least 10.6 MPa, satisfying the needs of field operations. Analyses of conductivity, XRD and SEM show that the working mechanisms of the retarder are the combined action of multipoint adsorption which controls the hydration of cement, inhibition of the growth of Ca(OH)2 crystals and complexation.