Given the serious noise accumulation and the nonlinearity effect in transoceanic fiber communication systems, probabilistic shaping (PS) and subcarrier multiplexing (SCM) are combined to alleviate transoceanic transmission link impairments, so as to improve the transmission performance of these systems. The single-carrier and dual-subcarrier multiplexing systems are simulated by developing a simulation link of transoceanic fiber transmission with the commercial software VPI. The simulation results show that the transmission distances of the uniform (H=4) and PS (H=3.6, H=3.7, H=3.8) dual-subcarrier PDM-16QAM systems are respectively 2.3% (405 km), 21% (3698 km), 19.7% (3468 km), and 14.5% (2549 km) longer than that of the uniform (H=4) single-carrier PDM-16QAM system under the 20% forward error correction (FEC) threshold. Then, an experimental fiber loop transmission platform is built to verify the feasibility of the proposed scheme. According to the experimental results, the transmission distances of the uniform and PS (H=3.8) dual-subcarrier PDM-16QAM systems are respectively 5.6% (282 km) and 46.2% (2323 km) longer than that of the uniform single-carrier PDM-16QAM system under the 20% FEC threshold. In summary, both simulation and experimental results demonstrate that applying PS and SCM to transoceanic fiber communication systems can effectively enhance these systems' transmission performance.