This study is to evaluate the individual angulation on maxlliary sinus projection and establishing angulation in children by new geometrical method. There were two groups, which are 60 cases in children (ranged from 1yr to 3yrs, 3yrs to 8yrs, 8yrs to 12yrs) and 50 cases in adults. We analyzed the true lateral maxillary sinus film of total 110 patients using new geometrical method. We demonstrated an angle of maxillary sinus projection. Arithmetical average angulation in adults is 36.56 degrees that accord with Waters. Whereas it is not valid during development of facial bone in childhood. The individual range of angulation according to age was that 1yr to 3yrs is 50-47 degrees, 3yrs to 8yrs is 47-40 degrees, 8yrs to 12yrs is 40-38 degrees. This geomatrical method will be useful in establishing angulation for maxillary sinus profection.