Reducing the complexity of soft-decision (SD) decoding algorithm or improving the performance of hard-decision (HD) decoding algorithm becomes an emerging trend on forward error corrections to ensure reliable optical transmission with high performance and low cost. In this paper, a hybrid decoding algorithm is proposed for staircase codes (SCCs), which performs HD decoding with the help of channel soft information via multi-level bit-marking (MLBM). The HD and SD in the proposed MLBM decoding algorithm isweakly hybridthat the soft information is only used for one-shot bit marking and does not involve in the decoding directly, thus providing good performance-complexity tradeoff. The marked bits indicate four reliability levels that are used to prevent miscorrections by checking conflicts with highly reliable bits and to enhance the error-correcting capability of the HD decoder by flipping unreliable bits. Particularly, three priority levels are set for bit flipping by combining with the decoding statuses of the associated component codes. The decoding results will, in turn, help to update the marked bits among the four reliability levels. Numerical results show up to 1.22 dB gains with steeper waterfall region and lower error floor when compared to conventional HD decoding for SCCs, at the cost of approximately a two-fold increase in the memory storage.