The synchronization of power generators is an important condition for the proper functioning of a power system, in which the fluctuations in frequency and the phase angle differences between the generators are sufficiently small when subjected to stochastic disturbances. Serious fluctuations can prompt desynchronization, which may lead to widespread power outages. Here, we derive explicit formulas that relate the fluctuations to the disturbances, and we reveal the role of system parameters. In particular, the relationship between synchronization stability and network theory is established, which characterizes the impact of the network topology on the fluctuations. Our analysis provides guidelines for the system parameter assignments and the design of the network topology to suppress the fluctuations and further enhance the synchronization stability of future smart grids integrated with a large amount of renewable energy.