is there any specific period the Sun Island Park open? or it is open along the whole year?

No, as I know, it opens in the whole year. In usual time, the opening hours are from 08:00 to 17:00. During the snow sculpture expo (Jan. 5-end of Fed), the opening time would be changed (usually 08:30 - 19:00). You can keep close attention to the news if going by then.