This paper uses the data collected from northwest China to describe magnitude of the private tutoring in rural primary school students，and estimate the impact of private tutoring to student academic achievement by DD(difference in difference)and DDM(matching difference in difference)approach.We find that students with lower testscore participate in private tutoring more than other students；the level of father's education and family wealth positively correlates with the length of tutoring time.Moreover，private tutoring does not significantly increase test-score.Reasons might be the limitations of teachers' qualification，the poor contents and organization of tutoring and the teachers' motivation to provide tutoring.Therefore，we suggest that governments should manage and control extracurricular tutoring activities properly，and provide high quality tutoring service to rural students，so as to narrow the education gap between rural and urban China.