Quasi-Zenith Satellite System (QZSS) is expected to provide a high accurate positioning service and allows two-way communication which includes the terminal location and short messages. For QZSS short message spread-spectrum code-division multiple access (SS-CDMA) communication, Flag Method was proposed as access control scheme. It is always able to communicate in optimum state which channel efficiency of 36.8 % is best. However, the channel efficiency is low even in optimum state. In this paper, we propose reservation channel (R-Ch) as an access control scheme which improves the upper limit of channel efficiency. In R-Ch, collision due to random channel selection is suppressed by selecting channels in multiple steps, and the channel efficiency is improved up to 84.0 %. Time performances of accommodating 3 million mobile terminals when using Flag Method only and Flag Method with R-Ch are shown. Flag Method with R-Ch can reduce the time by half compared with Flag Method only.