Random copolymerization is a simple and effective method to regulate and improve the performance of conjugated polymers. Herein, random copolymerization is employed to finely tune the transport behavior of terpolymers by side-chain engineering and BIBDF (bis(2-oxoindolin-3-ylidene)benzodifurandione) incorporation. Two series of terpolymers have been synthesized by varying both the branching positions, in the side chain, and BIBDF content, in the main chain. The spectral absorption, aggregation ability, electrochemical behavior, microstructure, and electrical performance in organic field-effect transistors have been systematically studied. The results reveal that the aggregation strength, lamellar packing, and it pi-pi interaction of the molecules can be enhanced by moving the side chain branching positions away from the backbone, which resulted in enhanced mobility. Furthermore, the influence of BIBDF content is studied under the optimal side chain, which indicates that an optimal amount of BIBDF can promote the molecular packing, crystallinity, and electrical properties of the terpolymers. For instance, the C33P2.5 polymer, with an optimal side-chain branching position and BIBDF content, exhibited a maximum mobility of 7.01 cm(2) V-1 s(-1), which is three times higher than the reference polymers, C11P3.7.5 and C30P0. The current study presents a novel route to maximize the performance of conjugated terpolymers and provides a baseline for further research on high-performance conjugated polymers for a wide array of applications.