When on a 12 months working visa from Kenya to China do I have to validate my visa every month?

Peter, do you hold a Z type? If yes, you don't need to validate it every month. After your arrival in PRC, you can apply for a temporary residence permit at the local exit and entry administraiton which may be valid for one year. With this permit, you can stay for a long time in PRC without going out to validate another allowed stay duration.