After breaking up, my girlfriend often harassed me. Is this illegal?

Illegal, according to the provisions of China's public security management punishment law.

Article 42 Whoever commits one of the following acts shall be detained for not more than five days or fined not more than five hundred yuan; If the circumstances are serious, they shall be detained for more than five days and less than ten days, and may be fined up to five hundred yuan:

(1) writing threatening letters or threatening the personal safety of others by other means;

(2) publicly insulting others or fabricating facts to slander others;

(3) fabricating facts, falsely accusing and framing others, and attempting to subject others to criminal investigation or public security administration punishment;

(4) Threatening, insulting, beating or retaliating against witnesses and their close relatives;

(5) sending obscene, insulting, intimidating or other information for many times to interfere with the normal life of others;

(six) voyeurism, sneak shots, eavesdropping, spreading the privacy of others.

You can call the police to the public security organ, which will take care of it.