A novel Null-type sampling nozzle with six sampling holes was developed to measure the particle concentrations and size distributions in high-pressure natural gas flows under isokinetic sampling conditions. The isokinetic sampling performances of sampling nozzles were investigated by experiments and numerical simulations with standard kappa-epsilon turbulent model. The maximum deviation between the experimental and numerical data was less than 4%. In order to ensure reliability and stability, sampling nozzles were calibrated in standard wind tunnel. Furthermore, this novel Null-type sampling nozzle was used to measure the separation efficiency of filter with an operation pressure of 6.0 MPa in a natural gas compressor station. The results of experiment and numerical simulation show that the new Null-type sampling nozzles have relatively smaller isokinetic sampling errors and reliable sampling efficiencies, which enable it competent to sample high-pressure natural gas. (C) 2008 Elsevier Ltd. All rights reserved.