In this study, in the region of Artvin, distribution of trees by diameter classes investigated in the even-aged and pure Oriental Spruce (Picea orientalis (L.) Link.) stands by site index and age classes. In the EasyFit (R) program, 60 different probability density functions are used to study of the distribution of diameter classes of trees in stands. For checking compliance of these models, Artvin, Ardanuc and Savsat Forest Management Directorates, 388sample plots were taken from the data were used normally closed stands. Diameter distributions have been fitted as Weibull (3P) in III, IV, V and IV. age classes, as Johnson SB in II, VI and VIII. age classes, and as Beta in VII. age class. Also diameter distributions have been fitted as Beta in I and II. site classes, as Johnson SB in III. site class, and as Weibull (3P) in IV and V. site classes.