The deep sea mud lifting system plays a critical role in the Riserless Mud Recovery （RMR） drilling process. In order to enhance the safety redundancy and adaptability of the lifting system， in-depth research on the multi pumps series parallel mechanism was conducted， including the detailed study of the series parallel structure design and working principle of the mud lifting pump， and the relationship between flow rate and lift during series and parallel operation， as well as the mathematical method and graphical method for series parallel operating points of the pump group. Furthermore， by utilizing the measured characteristic curve of the model pump， the Q-H characteristic curve and operating points of the dual pumps series parallel operation were obtained using graphical method. Finally， suggestions for dual pumps collaborative control were proposed.