This paper presents an improved particle swarm optimisation embedded tabu search for hydro unit commitment problem, which is decomposed into two sub-problems: unit commitment and economic dispatch. The unit commitment sub-problem determines on/off status of generating units with discrete variables, which can be solved by discrete binary particle swarm optimisation (PSO). The economic dispatch sub-problem determines the allocation of system load demand among the committed units with continuous variables, which can be solved by standard PSO. The two subproblems are run in parallel because they are interrelated. To avoid entrapment in local optima in solving the problem, the flexible memory system of tabu search (TS) is embedded into PSO to keep particles’ diversities in swarm for enlarging the search space and enhancing convergence property. The proposed method is applied to solve the unit commitment problem of Wujiangdu hydropower station. The experimental results reveal that the proposed method outperform...