7.A(4,0)是椭圆的右焦点，A'(-4，0)是椭圆的左焦点。|MA|+|MA'|=2a=10,|BA'|=2√10，|MB|<=|MA'|+|BA'|,当M,A',B三点共线时取等号。∴|MA|+|MB|的最大值=10+2√10.
