Djimon Hounsou is dragging his baby mama, Ri'za Marie Simpson, to court to fight over custody and child support ... months after she was arrested for alleged assault ... TMZ has learned.

According to court docs, obtained by TMZ, the "Gladiator" actor filed papers in late January seeking joint legal and physical custody of their two kids -- a son born in 2022 and a daughter born in 2023.

In response, Ri'za agreed to shared legal custody but argued that she should be awarded primary physical custody -- given their respective employment and travel histories.

She also asked for financial support since the breakup had a “significant impact on her finances.”

As TMZ first reported, Djimon contacted Atlanta police in December, claiming Ri'za hit him in the face after he asked her to leave his home.

Ri'za was arrested on charges of simple assault and obstruction for allegedly providing false information to officers.

After the arrest, Ri'za obtained a temporary restraining order, but later dismissed it after reaching an agreement with Djimon.