A method of metering the rate of flow of a dye solution from a spray nozzle for dyeing an elongate fabric material comprises spraying a test liquid equivalent to the dye solution over a plate member impervious to liquid, accumulating the test liquid and measuring the rate of its flow per unit length of time, thereby evaluating the performance of the spray nozzle. The rate of flow of such test liquid is simulated for actual dyeing operation to pre-adjust the jet pressure of the spray nozzle and/or the spaced of feed of the fabric material so as to attain uniform intensity of color on the dyed material.