Abstarct: In a live systems of biological damage caused by radiation occurs at three levels of molecular, cellular and organic. Radiation of the ionizing changes the cell’s molecular structure and disrupts its function. Brachytherapy by Gamma (_^192)Ir is one of the most widely used methods of radiation therapy in cervical cancer. For this reason, in the reaserch, we investigated the damage into the DNA molecule by photons and secondary electrons of the source at different distances, and then we obtained the doses rate in the defined dimensions of DNA. Also in the dosimetry, the environment around the water source is considered. But to achieve a proper treatment outcome, using water for all body tissues can be one of the sources of error in delivering the correct dose to the tumor. Hence the comparison of the use of soft tissue phantom (with density 1.04 g⁄〖cm〗^3 ) and muscle tissue (with density 1.05 g⁄〖cm〗^3 ) versus water phantom. In this way, In this work, we by using the MCNPX code calculate the flux and photon and electrons dose from iradium-192 Brachytherapy, in approximate dimensions of DNA in a water phantom and using the electron flux obtained, through the code MCDS has been investigated the efficiency of DNA breaks at different distances from the source. The simulations showed that the electron flux in some of the energies has peaks, which shifted to less energy as the distance from the source peaked, and also increased their width due to the combination of peaks and the removal of lower energies. DNA damage varies from source to diffraction and depends on the number of secondary electrons reaching that area and their energy, As the distance from the source increases, the values of the probability distribution function are reduced by the single-stranded and double-stranded DNA breaks. It was also observed that these values have peaks at all source. The maximum probability of a single-strand break at intervals 0.04, 0.1. 1 and 2.5 cm from the source inside the phantom of water respectively is 8.06%, 6.12%, 4.9%, 3.9% and maximum probability of a double-stranded break at these intervals is respectively 0.54%, 0.28%, 0.21%, 0.11%. It is noteworthy that the amount of dose rate reached by DNA with the assumption an activation of the 1 mCi using tali *f8 was reduced exponentially at these intervals and respectively is 27.202, 3.074, 0.026, 0.005 mGy⁄h. Considering with the soft and muscle tissue the same trend is observed in the flux volume graph, dose rate probabilities of breaks of the DNA strand, but by comparing these tissues with water, it was observed that, at a slight approximate distance, the percentage of differences in the use of phantom Soft tissue and muscle are replaced by water, but with increasing distance from the spring, these differences increase. According to the results, the maximum percentage of relative flux volume of photons and electrons in soft tissue was 1.71% and 6.6% respectively, and in muscle tissue is 3.33%, 11.8% and the amount of dose rate reached the soft tissue in comparison with the water phantom was observed with the highest percentage of relative difference of 1.96% and muscle tissue, with a percentage difference of 96.9% (all of which were at a distance of 2.5 cm from the spring).