Abstract: The fracture density model for the pelite reservoirs in several wells in the Gaojiaya oil field,Xinjiang is presented by means of the regression analysis of variable parameters.The mean relative errors of the model only reach 13.5%.So its precision is higher than those of the regression analysis of constant coefficients and BP network model.The mean relative errors of'the latter two are 38.7% and 17.9%,respectively.The data available have re-vealed that vertically the fracture densities decrease from 0.78 through 0.5 to 0.3 per me-tre as a function of depth and age(from late and early Middle Piiocene to Miocene),and horizonally the fractures tend to be most developed along the structural axis.The mean fracture densities range from 0.58 to 0.6 and to 0.3 per metre,respectively in the upper and lower Plioeene and Miocene strata of the oil field.