There are several possible reasons why a cat's urine might have a strong odor:

Cat litter not being changed for a long time: The excrement in the cat litter ferments excessively, producing a sour smell.
Urinary tract infection: Cats' urine contains bacteria and inflammatory secretions, which can cause an unpleasant odor.
During estrus: Cats secrete more hormones, which makes their urine smell stronger.
If your cat's urine has a strong odor and lasts for a long time, it is recommended to take your cat to a veterinary hospital for examination and treatment as soon as possible.