The conversion from constant current (CC) to constant voltage (CV) is one of the key technologies of CC underwater observatory systems. A shunt regulator with high stability and high reliability is usually used. Applications, however, are limited by high heat dissipation and low efficiency. In this paper, with an improved shunt regulation method, a novel concept of stepless power reconfiguration (SPR) for the CC/CV module is proposed. In cases with stable or slowly changing load, two modes of CC/CV conversion are proposed to reduce unnecessary power loss of the shunt regulator while being able to retain any operator-preset power margin in the system: (1) the manual SPR (MSPR) method based on single-loop control method; (2) the automatic SPR (ASPR) method based on inner-outer loop control method. The efficiency of the system is analyzed. How to select some key parameters of the system is discussed. Experimental results show that MSPR and ASPR are both effective and practical methods to reduce heat dissipation and improve the efficiency of the CC/CV module, while the high stability of the shunt regulator remains.