WA police's extensive investigation into a West Australian child porn ring has resulted in another man being charged with a string of child sex abuse.

Detectives from taskforce Mirzam claim a 62-year-old man from Beckenham sexually assaulted a seven-year-old girl over almost two years whilst he was in the company of the three people previously charged in relation to the alleged child porn ring.

Now four people face scores of child sex abuse charges over an alleged child porn ring in Western Australia.

He has been charged with nine counts of indecent dealing with a child under 13 years and two counts of sexual penetration of a child under 13 years and will front Perth's Magistrates Court on Wednesday.

The alleged offences happened between December 2013 and October 2015.