You use indefatigable to describe someone who never gets tired of doing something.
例句
His indefatigable spirit helped him to cope with his illness...他不屈不挠的精神帮助他对抗病魔。He was indefatigable in his efforts to secure funding for new projects.他不知疲倦地努力为新项目寻求资金。
英英词典释义
Adjective
1. showing sustained enthusiastic action with unflagging vitality;
"an indefatigable advocate of equal rights""a tireless worker""unflagging pursuit of excellence"