It is of great significance to find the ultra-rapid preparation technology of materials and realize the optimization of electroacoustic transport properties in the research of thermoelectric materials. In this study, BiAgSeS compounds were successfully prepared by self-propagating high temperature synthesis (SHS), of which the kinetic process was systematically studied. It is found that the melting of Bi is the key to activate and initiate SHS reaction. In addition, the high concentrations of nano- and atomic-scale strain field regions, and screw dislocations produced in the non-equilibrium SHS process provide an everlasting step source for material growth and make the grains possess the layered structure. In the process of material densification, the step source continues to play a role in dominating grain growth, and thus leaving nanopores at the grain boundary. Because of these defects, compared with samples via melting-quenching (MQ) combined with plasma activated sintering (PAS), the SHS+PAS samples can slightly increase the electrical conductivity and significantly reduce the lattice thermal conductivity by ~6%. Finally, the thermoelectric properties are optimized, and the ZT is improved in the whole temperature range with the maximum value of 0.5 obtained at 773 K.