Spare parts inventory management differs from other manufacturing inventory managements mainly due to its speciality in function with maintenance. Furthermore, spares demand management shows more complexities and differs from other productions’ SCM (Supply Chain Management). Recently, studies on information sharing in SCM attract more and more researchers’ attention because of its ability to counter the so-called “bullwhip effect”. Based on the authors’ consultant experiences and studies in practice, information sharing also plays a pivotal role on optimizing the effectiveness of the spares demand system. However, discussions those stand in the point of spares optimization management are limited, which should be a better combination of practical as maintenance engineers and managers making decision support for spares management. Therefore, this paper aims to help them to understand the information sharing in a spares demand system, to illuminate how to optimize the systems’ performance with it, and to elaborate how to improve information sharing process itself. First, a spares demand system was promoted, and information sharing in the system was investigated from a downstream and an upstream process separately. Second, performances of information sharing in such spares demand system were discussed from both qualitative and quantitative viewpoints. Third, the effective ways regarding information sharing utilization to optimize the spares demand system came into question. And finally, how to improve information sharing process in the mentioned system was discussed.