Abstract: A new method is proposed based on the Tikhonov regularization principle and se-lected weight fitting thought and precisely known reference station coordinates,to work out the regularized matrix,which can mitigate the ill-condition of the normal matrix.The rela-tive float ambiguity can be computed only using several epochs ' data.Combined with the LAMBDA method,the new approach can fix the integer ambiguity correctly and quickly.Taking an example,using measured data sets coming from the four medium-long baselines,the new method can obtain the exact ambiguities only usingL1-frequency data of five epochs.Compared with the existing methods,the new method can solve the ambiguities of medium-long baseline GPS network RTK only usingL1-frequency GPS data reliably.In practice,it can save the cost for fast positioning by GPS and would be applied widely.