Jasper, a two year old domestic shorthair, was shot at close range in the attack which took place in Oswaldtwistle, near Accrington in Lancashire on April 10.
According to inspectors, pellets entered his left eye, the roof of his mouth, abdomen, neck and two more pellets entered behind his left knee.
His lower leg bones were shattered which meant his left hind leg had to be amputated by vets.
The RSPCA is now appealing for anyone who might have information on what happened to come forward.
On the night of the attack Jasper returned to his home between 8pm and 9pm.
RSPCA inspector Nina Small said: “Poor Jasper, he could only make it through the first cat flap, and when the owners opened the door the cat walked in and fell in his cat basket. He would’ve been in a lot of pain.
"It is thought the timid pet who usually doesn’t venture far from home may have been at nearby allotments or the school playing field when he was attacked.
"Jasper is now recovering after suffering a terrible ordeal and will return to the vets at a later date for check-ups.
"Unfortunately the pellet behind his left eye could not be removed and vets will monitor this closely."
“Every year the RSPCA receives almost 1,000 calls to investigate cases and help hundreds of animals that are the defenseless victims of air gun attacks.
“It is very distressing to think that people take pleasure in causing such horrific injuries to defenceless animals. These are deliberate and brutal acts of cruelty.
“Cats and wildlife are normally the animals that are more susceptible to these incidents simply because they are out in the open with no one to protect them. Unfortunately, air rifle attacks are not as rare as we would like. The injuries caused by such attacks are horrific and often fatal.
"We are supporting Cat’s Protection’s call for tighter controls on air weapons. This, along with better education and explanation of the law when buying an air gun, and requirements that everyone must receive basic safety training before being allowed to walk out of the shop could help relieve the problem.
“These weapons cause horrific pain and suffering and it is illegal. Anyone caught deliberately using an air gun to injure an animal can be up to six months in prison and/or a £20,000 fine if found guilty under the Animal Welfare Act."
Anyone with information regarding this incident can contact the RSPCA on 0300 1234 999.