In order to solve the problems that flowmeters can′t  meet processing requirement in extension and renovation of caprolactam plant, changing parameters of the transmitters make measurement accurate without replacing new instruments . With differential pressure，vortex，electromagnetic flowmeters as examples respectively, according to various kinds of calculation principles for various kinds of flowmeters, new parameters for flowmeters′range changing in caprolactam plant expansion were calculated.The practical application showed that from 2002 while the flowmeters′range was changed in extension and renovation of caprolactam plant to now, the flowmeters have been running smoothly in practical application.