During the process of oil and gas exploration and development, the cementing operation is the key factor to ensure oil well productivity, and the performance of additives is directly related to the success or failure of cementing. In this study, the polymer retarder PID-1 was synthesised by aqueous solution polymerisation; the chemical structure, thermal stability and microstructure of PID-1 were studied by infrared spectroscopy, thermogravimetric analysis and scanning electron microscopy. In addition, the retarding effect and mechanism of PID-1 were analysed based on low-field nuclear magnetic resonance analysis, adiabatic calorimetry and scanning electron microscopy. Then, the polymer/organic compound high-temperature retarder PID-2 was constructed by adding organic compound PN with well retarding property; the retarding effect, thickening property, temperature and dosage sensitivity of PID-2 were then investigated. Combined with porosity evolution, type and content of hydration products, the internal mechanism of retarder PID-2 in relation to early mechanical strength development of the cement slurry system was revealed.