We propose and experimentally demonstrate a novel dual-channel polarization shift-keying (PolSK) optical transmission system, in which two semiconductor amplifiers (SOAs) are cascaded as two individual all-optical polarization modulators for each channel. The formed PolSK signals have four states of polarization (SOP), constituting two orthogonal binary data channels. Each channel can independently transmit data streams with different formats, bit rates and clock signals. The transmitted PolSK signals can be directly detected, it greatly simplifies the design of the receiver and eventually reduces the system cost. With this scheme, the system capacity for data transmissions can be doubled. Furthermore, due to the constant optical power of PolSK signals, the transmission system can enhance its tolerance to nonlinear effects in the fiber link, increase its long-distance transmission capacity. The SOPs of received signals are easily tracked by using two polarization stabilizers in each branch of the receiver, respectively, in order to achieve a stable signal receiving. The experimental setup based on the proposed scheme was constituted and several basic experiments were carried out for investigating the system’s performance. The long-distance data transmissions over 50 km, 80 km and 100 km fiber links, respectively, are carried out and the experimental results prove that the feasibility of our proposed scheme is validated.