Abstarct: The effect of environmental forces on rocks causes to create weakness levels in them, and the intersection of these plates is with each other that converts rock mass into separate blocks. The most basic factor determining the instability situations of the rock mass against the structures and construction within the rock is the reliance situation of each block. The construction of a structure such as a tunnel in a rock mass with several discontinuities can cause rock blocks to be released in different sizes. The blocks with the lowest level of reliance have the most critical of deployment way. The collapse and slipping the blocks will cause destruct to the spaces around the tunnel. One of the most well-known partial equilibrium methods used in the past thirty years is the method of key blocks analysis or block theory. The block theory examines the displacement of rocky blocks and the partial equilibrium analysis of these blocks from different excavation surfaces. The block theory method for structural analysis of deflection tunnels blocks of Pir Taqi Dam has been investigated in this study. For this purpose, the confidence coefficient, the fracture pattern, and the volume of the blocks are obtained and then the key blocks are identified using the structural discontinuities of the rock mass along the tunnel by Easykbt software. Direction to drill an underground structure in a jointed rock is the direction in which we encounter the least volume of unstable blocks in the wall and ceiling of the structure. For this purpose, block theory analysis has been carried out for 7 directions, which they have difference ( 30) relative to the direction selected by the project's consultant engineer. The most optimal direction for the water diversion tunnel of Pir Taqi Dam has been proposed considering the volume of unstable blocks formed in each direction N35 and also considering the use of the tunnel . Probabilistic analysis leads to a better understanding of sustainability and provides complete information on the stability of drilling excavations. One of the difficulties in estimating the probability of failure in underground excavations is the complexity of mathematical calculations. The Crystall Ball software that is a statistical software baxsed on the Monte Carlo method is used in order to analyze the probability of block stability. The probabilistic analysis of the safety coefficient of blocks is compared with the results of the block theory method. The results show that despite the fact that the block theory method refers to the stability of rocky blocks, but the results of the probabilistic method show the failure of blocks with a particular probability. Ultimately, the structural analysis of the block was performed with the Unwedge software on the proposed optimal path and the largest unstable wedges were identified. The maintenance system has been then designed to stabilize these wedges. The results show that with the execution of a 5cm thick Shotcrete in the upper half of the tunnel, as well as the execution of mechanical rock bolts with a length of 6 meters and a 1.2 * 1.2 distance in the tunnel roof, cause to the stability of the unstable wedges in this direction.