The invention discloses a method and device of building a decision-making tree and a method and device of network performance optimization. The method of the network performance optimization comprises the steps of obtaining preset current parameter data of wireless parameters in a wireless network to be optimized; forecasting a network performance level of the wireless network according to a wireless parameter decision-making tree of the wireless network and the obtained parameter data; judging whether the wireless network needs performance optimizing or not according to the forecast network performance level; and if a judging result is yes, the parameter data of the wireless parameters conduct adjusting so as to optimize network performance of the wireless network. By the adoption of the technical scheme, the problems that in the prior art, flexibility of network performance optimization is low, and a process is complex and lags are solved.