Variations of air core size, discharge coefficient, spray angle and breakup length for simplex-type swirl atomizers are examined from the images of air core and spray shape, and the results are compared with previous theoretical results. The air core size and spray angle increase with the increases of the injection liquid flow rate and geometric constant. On the other hand, the discharge coefficients decreases with the increases of the injected liquid flow rate and geometric constant. By increasing the flow rate, the breakup length first decreases and then slightly increases up to a certain value in the low injection flow rate. With further increase of the flow rate, breakup length slightly decreases again. At the higher flow rate, the breakup length increases up to a maximum value and then finally decreases. Also, the larger geometric constant exhibits the shorter breakup length.