Killing a cat is illegal or not needs to be based on the following circumstances:

1, if the killing of stray cats, generally is not enough to become a crime, because our country's criminal penalties and does not stipulate that this behavior belongs to which kind of criminal behavior;

2, but if it is a cat raised by others, the value of the higher reach to the loss of other people's property is likely to constitute a crime.

"Chinese People's **** and State Criminal Law" Article 275

Willful destruction of property crime willfully destroy public or private property, the amount of larger or other serious circumstances, shall be sentenced to fixed-term imprisonment of not more than three years, detention or fine; the amount of huge or other particularly serious circumstances, shall be sentenced to fixed-term imprisonment of not less than three years and not more than seven years.

Article 260

The crime of cruelty abuses a family member, and if the circumstances are aggravated, the offender shall be sentenced to fixed-term imprisonment of not more than two years, criminal detention or control.

Whoever commits the crime in the preceding paragraph, causing serious injury or death to the victim, shall be sentenced to fixed-term imprisonment of not less than two years and not more than seven years.

The crime of the first paragraph is dealt with only if it is told, except when the victim is incapable of telling, or is unable to tell due to coercion or intimidation.