Bacterial foraging optimisation (BFO) is a commonly adopted bio-inspired optimisation algorithm. However, BFO is not a proper choice in coping with continuous global path planning in the context of unmanned surface vehicle (USV). In this paper, a grid partition-based BFO algorithm, named AS-BFO, is proposed to address this issue in which the enhancement is contributed by the involvement of A* algorithm. The Chemotaxis operation is redesigned in AS-BFO. Through repeated simulations, the relative optimal parameter combination of the proposed algorithm is obtained and the most influential parameters are identified by sensitivity analysis (SA). The performance of AS-BFO is evaluated via five sizes grid maps and the results show that AS-BFO has advantages in USV global path planning.