Correct resolution of ambiguities for GNSS reference network is prerequisite for generation of corrections for network RTK. Due to the presence of atmospheric delay in the double-differenced observations, the convergence time of ambiguity is about a dozen minutes and even dozens of minutes for medium and long baselines. And in the case of loss-of-lock or new rising satellites, the integer ambiguities have to be redetermined over and over again. But for the application of GNSS network RTK, the resolution of ambiguity needs to be determined real time as possible. Atmospheric delays of previous epochs are used to predict atmospheric delays of following epochs, and then wide and narrow lane combination of carrier-phase observations as well as ionosphere-free combination is used to resolve ambiguities with single epoch. Our test results show that the precision of predicted double-differenced tropospheric and ionospheric delays is about 2-3 cm using temporal-and spatial-correlation exponent model, and the success rates of L1 ambiguities resolution with single epoch reach above 90% for medium and long distance GNSS reference station network.