U.S. District Judge Loretta Preska said the two series will have to coexist - as did shows like "The Honeymooners" and "I Love Lucy," or "Bewitched" and "I Dream of Jeannie."
While blatant copying is a no-no, network programming has been "a continual evolutionary process involving borrowing frequently from what has gone before," the judge said, summarizing testimony presented in a Manhattan courtroom for two days last week.
CBS sued ABC in November to stop the show from airing.
Preska said ABC's new show - "I'm a Celebrity ... Get Me Out of Here!" - seems different enough that CBS is unlikely to prove ABC copied its hit "Survivor."
"Both shows combine well-known and frequently used elements of earlier works," she said. "Each series also includes well-known elements not in the other."
ABC's parent company hailed the ruling. "We're delighted with the court's decision, which we believe is entirely correct, and look forward to giving the American public a chance to see this fresh new reality show," said John Spelich, a spokesman for The Walt Disney Co., which owns ABC.
In a statement, CBS said: "The judge ruled that due to its quality and tone, the ABC program is substantially different than `Survivor.' We respect the ruling and are now studying our options."
In its lawsuit, CBS said the ABC show could irreparably damage the network, which rose from fourth place to first in the ratings partly because of the enormous success of "Survivor."
But the judge noted the substantial harm that would be done to ABC if a show it was relying on during the critical February ratings sweeps period was halted.
She also discounted a CBS argument that it would be damaged because the rival show was blocking its own plans for a celebrity-driven reality series, saying those plans did not seem to progress until CBS learned of ABC's show.
The judge said ruling against ABC would "stifle innovation and stifle the creative process." She also cited many differences between the shows, especially in "concept and feel."
On "Survivor," 16 contestants in a remote location compete in challenges for food rewards and the right to stay on the show. One contestant is voted off the show each week, and the last person wins $1 million.
In the ABC show, eight celebrities would be put in a remote location, given tasks or trials to perform and be allowed to eat better food if they do well.
The judge said "Survivor" had a serious tone featuring "cutthroat competition." The ABC show, though, features humorous hosts and contestants merely fighting to be king or queen of the jungle, with any monetary reward being donated to their favorite charity, she said.
The judge said the lighthearted celebrity show with its unpolished video was no match for the serious "Survivor" with its movie-quality images and attention to detail.
By Larry Neumeister