I just bought this Asus 18x SATA DVD-E818A9T but I can not watch bluray movie on it.
In order to watch Blu Ray movie on PC you require a drive that supports Blu Ray Media, you also need decoding software that supports blu ray playback.
Based on the Part number you have provided above this appears to be a DVD Drive only and does not support the reading or playback of Blu Ray media.
https://www.asus.com/Optical-Drives-Storage/DVDE818A9T/specifications/