Abstract: The second subsea tunnel of Jiaozhou Bay(SSTJB) is now the longest highway subsea tunnel under construction in China. To ensure tunnel construction safety, this article summarized the primary unfavorable geology and analyzed the corresponding construction risks of SSTJB based on the literature review and field practices. The results showed that the geological condition of SSTJB was very complicated. Specifically, the primary unfavorable geology includes an active fault belt, soft and hard strata, and water-rich faults. When the subsea tunnel excavates in the above unfavorable geology by borehole-blasting method and shield method, there are the risks of water inrush, collapse, surface subsidence, shield jamming, docking and receiving of the shield machine, and construction of oversized receiving chamber. Moreover, the influence of the blast and surface subsidence on residential buildings, oil ports, and oil transportation pipelines also should be paid enough attention. During the construction, special attention must be paid to unfavorable geology and possibly induced engineering risks. Finally, the paper proposed corresponding engineering suggestions and research countermeasures for the above problems. It is suggested that scientific research should be carried out systematically in advanced prediction of unfavorable geology, safety control of passing the active fault belt, marine environment protection, risk assessment, emergency rescue technology system, and construction control of the super large cross-section etc. The relevant research can provide scientific basis for design and construction, and ensure tunnel safety during construction. Furthermore, it fills the core and key technical gap in the construction of deep and long subsea tunnels in China, and provides a basis for the subsequent construction of ultra-long subsea tunnels.