This paper proposes an optical communication and positioning method of underwater observation apparatus for environmental monitor using distance image sensor. The glass ball underwater observation apparatus is expected to realize the low cost monitoring system. We tried to apply the distance image sensor by CMOS to ranging in underwater environment by remodeling a retailed sensor unit. In the distance image sensor by CMOS on land application, both the emitter unit and the receiver unit are installed in a same board. However, the emitter unit and the receiver have to be installed separately in the case that the ranging is employed to measure the distance between the emitter on the sea surface and the receiver inside the glass ball. In the separate setting of the distance image sensor by CMOS, the accuracy of the measurement result is investigated. Additionally, influence of both the receiver unit angle relative to the emitter unit and the existence of the glass ball is also examined on the distance position. Finally, it is found that the proposed CMOS image sensor installation is valid highly in the underwater application.