Hybrid multi-terminal direct current (MTDC) transmission technology has been a research focus, and primary frequency regulation (FR) improvement in the receiving-end system is one of the problems to be solved. This paper presents a decentralized primary FR scheme for hybrid MTDC power systems considering multi-source enhancement to help suppress frequency disturbance in receiving-end systems. All the converters only need local frequency or DC voltage signal input to respond to system disturbance without communication or a control center, i.e., a decentralized control scheme. The proposed scheme can activate appropriate power sources to assist in FR in various system disturbance severities with fine-designed thresholds, ensuring sufficient utilization of each power source. To better balance FR performance and FR resource participation, an evaluation index is proposed and the parameter optimization problem is further conducted. Finally, the validity of the proposed scheme is verified by simulations in MATLAB/Simulink.