前者是“某人决定,打定主意”,后者是“改变某人的注意” e.g:He made up his mind to teach in the rural area.他决定到农村教学。 He changed his mind not to teach in the rural area.他改变了到农村教学的主意。(意思是不去了)
make up one's mind 是决定的意思,用法是make up one's mind to do sth.e.g:I made up my mind to give up going to college,我决定放弃上大学。 change one's mind是改变主意的意思。I changed my mind.我改变了我的主意。