The trial, which is one of the biggest of its kind in Sweden, got under way in the western city of Borås on Monday morning.
The defendant, who has not been named in the Swedish media, is accused of forcing more than 100 girls, mostly between the ages of 12 and 14, to undress and perform sex acts on camera.
His alleged victims come from across Sweden, from Nacka near Stockholm, to Malmö in the south and Umeå, the largest city in the north of the country.
The 45-year-old suspect is accused of using several fake online identities to lure the girls into chatting with him online, including via Skype and US-born social platform Kik.
Some of the victims are believed to have had long-running connections with him, while others quickly stopped chatting or blocked him from contacting them.
According to the TT news agency, the trial's start was significantly delayed because it took investigators months to trace all the evidence they needed from web servers, mobile phones and laptops.
Prosecutors are also expected to use files gathered from a computer owned by one of the suspect's former employers.
“They contain evidence where the victims masturbate in front of the camera and we will need to see a part of this in court,” said prosecutor Hedvig Lundblad in her request for the material ahead of the first hearing.
Most of the trial is expected to take place behind closed doors due to the sensitive nature of the allegations and the graphic evidence involving minors.