A phthalonitrile oligomer containing thioether bonds, namely, 4,4'-((((((2-cyano-1,3-phenylene) bis(oxy))-bis(4,1-phenylene))bis(sulfanediyl))bis(4,1-phenylene))bis(oxy))diphthalonitrile (BSDP), was successfully prepared via nucleophilic substitution reaction. The BSDP oligomer was polymerized with 4- (aminophenoxy) benzonitrile (APPH) and 4,4'-diaminodiphenyl (ODA) as curing agents. Structure of the oligomer BSDP was confirmed by ¹H and ¹³C NMR and Fourier Transform Infrared spectroscopy (FTIR). Differential scanning calorimetric (DSC) was used to study the melting point of the oligomer and their curing kinetics. The results show that the melting point of the oligomer is 86 ℃. The particular interatomic distances for two polymers were analyzed by Wide-angle X-ray Diffraction (WAXD), respectively. Thermomechanical properties of the polymers were investigated by Dynamic Mechanical Analysis (DMA), and thermal stability and thermal oxidation stability of the polymers were explored through Thermogravimetric Analyses (TGA). Under the atmosphere of nitrogen and air, the temperature of the resin losing 5% weight were 486.3 and 496.3 °C, respectively.