Abstract: In order to meet the demand for rapid dissolution, temperature resistance, and salt resistance of polymers in offshore oilfield development, the emulsion polymer with ultra-high relative molecular weight, rapid dissolution, temperature resistance, and salt resistance was prepared by low-temperature composite initiation system using self-made high efficient polymer emulsifier and heat stabilizer. In addition, the effects of the preparation process, cosolvent amount, functional monomer amount, and heat stabilizer amount on the performance of polymers were studied. The results show that the polymers with a relative molecular weight of 22–24 million can be obtained through process optimization. Urea and sodium sulfate can significantly improve the dissolution rate of the emulsion polymer with ultra-high relative molecular weight, temperature resistance, and salt resistance. Adding N,N-dimethylacrylamide, self-made heat stabilizer, and sodium 2-acrylamide-2-methylpropane sulfonate during polymerization can significantly improve the temperature resistance and salt resistance of the polymer. The structure and properties of the emulsion polymer with ultra-high relative molecular weight, temperature resistance, and salt resistance were characterized by electron microscopy, laser particle analyzer, gel permeation chromatography (GPC), and thermogravimetry (TGA). The results indicated that the prepared polymer has uniform emulsion particle distribution, narrow relative molecular weight distribution, and good temperature resistance. The viscosity retention rate of the emulsion polymer within 30 days was more than 90% at a salinity of 35 000 mg/L and temperature of 75 °C. The results reveal that the emulsion polymer with ultra-high relative molecular weight, temperature resistance, and salt resistance has the characteristics of rapid dissolution, high relative molecular weight, and good temperature resistance and salt resistance and can be widely used in offshore oilfield development by oil displacement.