Pourmousavi replaced Dariush Yazdi in the Ahvaz-based football club.
Under coaching of Yazdi, Esteghlal Khuzestan sits bottom of the table with four points from 12 matches.
Pourmousavi was without a team since being sacked by Foolad in September.
The 47-year-old trainer coached Esteghlal Khuzestan last year and led the team to 12th place in Iran 16-team league.
Esteghlal Khuzestan will host Esteghlal on Sunday.