The Iranian team overpowered host Bahrain 3-0 (25-18, 25-14, 25-18) on Wednesday at the Isa Sport City Hall C in Manama.
Pouria Yali scored 15 points for Iran, while Hasan Mohamed had nine points for Bahrain.
Iran will face Brazil in the competition’s semi-final Thursday night, while Italy will meet Russia.
The 2019 FIVB Volleyball Men's U-21 World Championship is being held i Bahrain from July 18 to 27.
A total of 16 teams from the 5 confederations compete in the tournament.