The nccessity and urgency of PDCbit downhole folw field testing are demonstrated according to the character of PDC bit structure,principle of rock fracturing and circumstances of using in drill sites.Combining withforeign informations ,an instrument was designed for PDC bit with single nozzle testing,Also used for downholeover flow characteristic and full gauge bit downhole fluidic rule experiments.This instrument realizedthreedimensional measurement of downhole folw field characteristics.