Previous works have shown that the suction probe cannot be used to accurately measure the upwardand downward particle fluxes independently.A new method using fa single optical probe to measure the local solidflux is presented. The measurement of upward, downward and net solid nuxes was carried out in a cold modelcirculating fluidized bed (CFB) unit. The result shows that the profile of the net solid flux is in good agreementwith the previous experimental data measured with a suction probe. The comparison between the average solid fluxdetermined with the optical measuring system and the external solid flux was made, and the maximum deviationturned out to be 22%, with the average error being about 6.9%. These confirm that the optical fiber system can besuccessfully used to measure the upward, downward and net solid fluxes simultaneously by correctly processing thesampling signals obtained from the optical measuring system. Previous works have shown that the suction probe can not be used to accurately measure the upward and downward particle fluxes independently. A new method using fa single optical probe to measure the local solid flux is presented. The measurement of upward, downward and net solid nuxes was carried out The results shows that the profile of the net solid flux is in good agreement with the previous experimental data measured with a suction probe. The comparison between the average solid fluxdetermined with the optical measuring system and the external solid flux was made, and the maximum deviation has been to be 22%, with the average error being about 6.9%. These confirm that the optical fiber system can be successfully used to measure the upward, downward and net solid fluxes simultaneously by correctly processing thesampling signals obtained from the optical measuring system.