Abstract: In order to solve the problems associated with complex deepwater environment, the riserless drilling system has been developed. As ocean riser is eliminated in this technique, cutings and mud are returned to the drilling platform through a small diameter hose from the seabed by the subsea pumps. According to parametric requirement of mudlift system and two-phased flow theory, parametric computation of mudlift system was conducted, and provided theoretical basis for the design of mudlift equipment of the riserless mud recoverydrilling. In the light of the above stated computational method, computation and research of parameter of mudlift systerm in 500 m water depth were carried out ,and parameter of cuttings’s influnce to parameters of mudlift systerm was analysed.