The 13-year-old was admitted to intensive care following a surfing accident in Malibu on July 17.
Schwarzenegger tweeted: "I knew Christopher couldn't be stopped! Big thanks to all the doctors, nurses & staff at UCLA that helped him recover."
Christopher is expected to make a full recovery from injuries thought to include broken ribs and a collapsed lung.
Schwarzenegger's estranged wife Shriver released a longer statement through her own Twitter account, saying: "Blessed to be able to take Christopher out of the hospital last night. What a feeling of relief to know that he's going to be fine. Thank you for all your thoughts and prayers. The whole family, especially Christopher, felt your love.
"We were very lucky. Many patients and families we met have been there so long and have no end in sight. I pray for their recovery. I will forever be grateful to the amazing doctors, nurses and hospital staff in the ICU who helped my son."
Schwarzenegger and Shriver have officially begun divorce proceedings following their separation in May.
Documents obtained by TMZ showed that the former governor of California had originally asked the court to decline Shriver's requests for spousal support and for Schwarzenegger to meet all legal costs.
However, the website has since published amended papers - filed five days later - which allow both of Shriver's requests.