6.2 mm。 A whirling jet fluid sprinkler was put forward. The working principle of the sprinkler was introduced. An orthogonal array of five factors and four levels was selected to carry out the experiment. The graduations of geometrical parameters which affected working conditions were achieved after the orthogonal experiment, which were diameter of cover plate for outlet, length of beeline sect, length of leadflow, offset length, length of working area, and pipe length in sequence. Their affects on water distribution, jet range and whiling speed were analyzed respectively. The best geographical parameters of sprinkler typed 10 were summarized. Diameter factors of cover plate for outlet were added to review its actions. The minimum diameter is 5.2 mm, the maximum diameter is 7.2 mm and the best geometrical parameter is 6.2 mm.  