Synthesis process of ZrAl3O3N was investigated by non-pressure sintering at 1600 oC in N2 atmosphere according to five drafted equations. The influences of the atmosphere and material combination on the synthetic effect of ZrAl3O3N were preliminarily discussed by XRD. The results showed that atmosphere was a key factor that determined whether ZrAl3O3N could be synthesized, i.e. ZrAl3O3N could only be synthesized in high purity N2 atmosphere, and that ZrAl3O3N was only synthesized on condition that the raw material composition included both AlN powder and nano-ZrO2 powder. However, with increasing of AlN content, the XRD peaks of ZrAl3O3N and ZrN phase gradually reduced, and pure ZrAl3O3N was hardly obtained by in-situ reaction between AlN and ZrO2 because of generation of ZrN as well.