Abstract: On the basis of the combined bias interpolation(CBI) method of GNSS network RTK,a modified combined bias interpolation(MCBI) method is proposed.MCBI computes the troposphere delay using the troposphere model and estimates the first order ionosphere delay.Then MCBI separates the combined bias into three parts: the first order ionosphere delay,the troposphere delay computed by troposphere model and residual error.The example shows that the precision of MCBI is higher than that of the CBI and very convenient to use.