Abstract: An Preventing-inactivation adaptive-step GSO (PA-GSO) is proposed to prevent firefly inactivation. The first step is non-linear decreasing method.The initial step is larger and the moving speed is faster, and the later step is gradually reduced to a fixed smaller value, which realizes the balance of precision and speed in algorithm. And then in order to cope with the firefly's neighbor with the empty set may lose the mobility, using the prevention of firefly inactivation mechanism to optimize the firefly movement. By comparing the GSO, A-GSO and CSGSO algorithms, the PA-GSO algorithm is further improved in optimization accuracy, convergence speed and stability.