Actively promoting the synergies between forest carbon sinks and biodiversity conservation is a crucial initiative for the world to address climate change and mitigate biodiversity loss. Drawing on the synergy theory, this paper elucidates the driving mechanisms of the synergy between forest carbon sinks and biodiversity conservation, analyzes the dilemmas faced by this synergy, and proposes an implementation strategy to resolve these dilemmas. The study finds that the driving mechanisms of the synergy between forest carbon sinks and biodiversity conservation are twofold: firstly, the development of forest carbon sinks has significant direct and indirect, as well as positive and negative, impacts on biodiversity, making it challenging to separate and develop them independently; and secondly, biodiversity conservation offers new opportunities for the sustainable development of forest carbon sinks. However, due to the difficulty of realizing the value of biodiversity conservation products independently, the high degree of regional overlap, and the lack of coordination and unification in the project's main body, the development of forest carbon sink projects is prone to damaging biodiversity, etc., resulting in the synergy facing price "failure", subject "disconnection", and process "inappropriateness". Consequently, the synergy between the two faces three major challenges: price "failure", subject "disconnection", and process "inappropriateness". For this reason, we should adopt "forest carbon sinks +" as the core concept, embed biodiversity protection as "private goods" in the carbon sink market, and encourage the transactional entities in the forest carbon sink market to expand into "carbon sinks+biodiversity protection" dual subjects, thereby forming a comprehensive forest carbon sink market. To promote the expansion of forest carbon sinks market trading subjects into "carbon sinks+biodiversity protection" double subjects, to form the biodiversity protection synergy in all aspects of forest carbon sinks project development, and to realize the synergistic development and integrated development of forest carbon sinks and biodiversity protection.