In a polarization-division multiplexing soliton system, the multiple soliton interactions are studied numerically, the effects of soliton interactions on timing jitter are analyzed, and a countermeasure using nonlinear gain to suppress the soliton interactions is developed with the help of computer modeling. It is found that the mutual interactions between neighboring solitons cause soliton transmission instability and lead to timing jitter. The interactions of more than two solitons are stronger than that of two solitons. Therefore, the maximum transmission distance limited by the soliton interactions should be inferred from the collision distance of multiple soliton interactions, not the mutual interactions of two solitons. Nonlinear gain combined with a filter is suggested to effectively suppress the soliton interactions and stabilize soliton propagation.