Riserless mud recovery drilling technology （RMR）， as one of the dual gradient drilling techniques， has the advantages of environmental protection， simple well structure， low engineering cost and high safety. However， as an emerging drilling technology， RMR has not seen any engineering application currently in China， and there is a lack of relevant field experience， though it is relatively mature in foreign applications. The most important thing is that the RMR control system has complex functions and high requirements for reliability， accuracy， and sensitivity. When faced with complex working conditions， the control system is required to respond promptly and accurately. Therefore， in order to develop the domestic riserless mud recovery drilling technology （RMR）， and to narrow or even surpass foreign drilling technology， there is an urgent need to make a relatively complete design of the control system. In this paper， in light of several typical working conditions in the drilling process with riserless mud recovery， analysis is conducted of the functions of the control system under different working conditions with the design of the specific realization form of the control function. It is desired that the research on the functional design and realization of the control system of the riserless mud recovery drilling technology can provide a useful reference for similar research in the future.