The top four runners in each of the initial seven heats automatically qualified for the second round. The next four fastest runners from across the heats also qualified. Those 32 runners competed in 4 heats in the second round, with the top three runners from each heat and the four next fastest runner qualifying for the semifinals. There were two semifinal heats, and only the top four from each heat advanced to the final.
Prior to this competition, the existing world and Olympic records were as follows:
No new world or Olympic records were set for this event.
The qualification period for Athletics was 1 January 2003 to 9 August 2004. For the men's 200 metres, each National Olympic Committee was permitted to enter up to three athletes that had run the race in 20.59 seconds or faster during the qualification period. If an NOC had no athletes that qualified under that standard, one athlete that had run the race in 20.75 seconds or faster could be entered.
Qualification: First 4 in each heat (Q) and the next 4 fastest (q) advance to the Round 2.
Qualification: First 3 in each heat (Q) and the next 4 fastest (q) advance to the Semifinals.