There was carried out the modeling of crystal lattices of AgBr - (TlBr0,46I0,54) system solid solutions, containing 0-100% (wt.) of TlBr0,46I0,54 (KRS-5) in AgBr. The modeling results showed the possibility of existence of stable solid solutions, containing up to 50.0% (wt.) (38% (mol.)) of KRS-5 at the room temperature. This was confirmed by investigation and construction of AgBr - (TlBr0,46I0,54) system phase diagram, which proved to possess the wide homogeneity area. The system, containing up to 50% (wt.) (38% (mol.)) of KRS-5 has a face-centered cubic lattice (NaCl type) in the temperature range of 0-135 оС. New diagram is characterized by the types of lattices, varying from face-centered cubic (NaCl type) to body-centered (CsCl type). Moreover, the new diagram is characterized by the presence of high temperature transitions field. The phase diagram was investigated by DTA and XRD methods (with the step of 10% (wt.)). There were determined the values of lattice parameters for a number of solid solutions, containing 20% (wt.), 35% (wt.), and 50% (wt.) of KRS-5, which corresponds to 5.799 nm, 5.834 nm and 5.866 nm of crystal lattice values. There were used the phase transition temperatures, registered under cooling conditions for phase diagram investigation since these values are usually used for the crystal growth regimes adjustment. There is experimentally shown the utilizing competence of the described diagram for searching of optimum crystal growth regimes in dynamic mode for Ag1-xTlxBr1-0,54xI0,54x solid solutions.