The influence of orbital errors of GPS geodetic network may became significant if the measured distances are greater than 50 km. The proper input covariance matrix is then required for the adjustment. In the paper the numerical method for finding this covariance matrix is described, based on the principle of randomization of errors of the model parameters. Some examples of application of this method are given for estimation of correlations between the baselines and for construction of the variance-covariance matrix for the 5 stations test network.