With the development of GNSS technology,the higher demand for calculation is put forward in the field of the whole network baseline solution.The conventional baseline solution is a three-step method,which is complex and relies on the success rate of ambiguity solution at each step.A modified strategy for baseline ambiguity resolution is proposed in the paper,using un-combined and un-differenced model.The equality constraint is also used to recover the integer property of ambiguities.By the constraint of the fixed ambiguities,the baseline solution could be obtained.The data sets from various lengths of baselines are conducted to investigate the performance of the UD strategy.Depending on the empirical fixed success rate and convergence time,the modified strategy has a better AR performance on the rising satellites and weakens the unknown coefficient of correlation between ambiguities.