It becomes vulnerable to face voltage instability incurred from over-utilized existing facilities or any contingency due to gradually increasing system load or regional electricity demands. A good generation direction (GD) can alleviate voltage instability and thus increase the loading margin (LM) for power systems to accommodate more power transfers. This paper proposes an optimal GD seeking method based on a particle swarm optimization (PSO) algorithm involving in the continuation power flow (CPF) process to compute the maximum LM. Three objective functions are investigated for possibly different purposes. They are maximum LM, minimum generation cost, and minimum generation cost and maximum LM at the same time. The results obtained with the three objectives and the cost participating factor (Cost PF) approach are compared each other to validate the proposed method.