Hydraulic fracturing is the best known method for determining the magnitude and direction of horizontal principal stresses in the deep earth; extensive studies have been conducted on its implementation and the parameters affecting its results, such as borehole diameter, pressure interval length, and fracture fluid viscosity. However, there are many ambiguous points about the hydraulic fracturing method. As a result, more studies are needed to determine the effect of various parameters on the process of the method. These studies require the design and construction of equipment and devices such as a real triaxial device. A real triaxial test device capable of performing hydraulic fracturing tests on a laboratory scale was designed and built at Shahrood University of Technology. In order to investigate the relationship between fracture pressure and two parameters, fluid viscosity and borehole diameter, which can affect the results of the hydraulic fracturing method in determining the stresses in the ground, hydraulic fracturing tests were conducted using this device. For this purpose, concrete samples measuring 30 x 30 x 30 cm, with holes with diameters of 50 mm, 30 mm and 80 mm in their centers, were tested. The results of these tests showed that with increasing borehole diameter, the fluid pressure for rock fracture decreases. In the second part, 3 types of hydraulic oils with different viscosities (68H, 64H and 100H) were used in this study. The results showed that with increasing fluid viscosity, the fracture pressure decreases.