The current paper describes the results of a systematic experimental study of the visible lengths of coal-derived syngas jet diffusion flames. A combustion system was designed to produce a uniform swirl diffusion flame, far comprehending the flame characteristics of coal-derived fuel. To determine the flame length characteristics of the flame, the nozzle diameter of the lab-scale combustor was varied at 1.23, 1.96, and 2.95 mm and the flame length of each condition was studied. The fuel gases used were various compositions of CO and H_2, simulating the composition of coal synthetic gases. The flame length characteristics of the simulated coal synthetic gases with different compositions were examined. The results of the experiment were compared with the characteristics of a pure methane flame using the dimensionless flame length, L^*. The calculated flame lengths were slightly lower than the actual measured flame lengths, and the flame length values for both cases were well matched with values obtained at the corresponding experimental conditions. Accordingly, within the experimental parameters of the current investigation, the flame length was mainly determined by the nozzle type of the combustor.