The mechanical properties of two-component crystalline random copolymers are primarily based on their microstructure. At the same time, the influence of the composition on the crystallization behavior and crystal structure of these materials is also well known. Thus, in this study, a poly (butylene succinate-co-butylene terephthalate) random copolymer (PBST) with different molar ratios of butylene terephthalate (BT) was prepared. A systematic analysis of the crystallization behavior, crystal structure, and mechanical properties of PBST with different BT contents was carried out using WAXD, SAXS, and DSC analyses. The investigations showed that PBST-37.5 containing 37.5 mol% of BT content had the lowest strength and highest elasticity among the different compositions. This was because the two-component crystallization of poly (butylene terephthalate) (PBT) and poly (butylene succinate) (PBS) was greatly inhibited at the corresponding BT composition and the crystal growth was the least perfect, imparting poor strength to the PBT-37.5. Alternately, when the content of BT was 32.5 mol% in the PBST, the PBS segment could crystallize, and both PBT and PBS crystals were formed in the PBST-32.5. Thus, PBST-32.5 showed a higher material hardness than PBST-37.5. In contrast, when the BT content was greater than 37.5 mol% in the PBST, only PBT crystals existed in the PBST copolymer. Further, as the BT content increased, the crystal size of PBT gradually increased, which led to a closer packing of the crystal arrangement, increasing the crystallinity. This led to a gradual increase in the strength of the PBST material and a gradual decrease in its elasticity.