The challenges online mathematics education faces in rural primary schools in China are systematic. This article addresses five aspects of the challenge. Poor infrastructure, poor signal, and backward network configuration in rural areas have caused students online access difficulties. Second, purchasing high-performance electronic equipment is a burden for many families due to poverty in rural areas. In addition, the learning facilitation in rural areas is weak; students need to cope with the rapid transition from traditional offline to online learning. When the drawing and tabulation required for learning mathematics are changed from manual to online, new operations and software must be learned, and both students and teachers need assistance. Finally, teacher-student interaction, assessment and feedback also present unique challenges for online mathematics education. These challenges include physical barriers brought by the external environment and psychological barriers that students need to overcome, which will widen the gap in mathematics achievement between urban and rural students, and some even affect all subjects. Therefore, eliminating these challenges or reducing their negative impact is an urgent task to narrow the urban-rural education gap.