Objective To analyse the risk factors for second femoral neck fracture after primary femoral neck fracture for aged . Methods Between March 2005 and September 2013, 36 patients who had the second fracture of the contralateral femoral neck after primary femoral neck fracture ，as the observation group. 104 patients for primary femoral neck fracture as the control group.Compared the two groups，observe the relevant indicators，include the cause of injury，sex, age，Singh index，related complications，function of contralateral joint . Results The direct cause of all patients for the observation group and 89.42% for the control group was falling（Ρ>0.05）; the mean age of the observation group and the control group were (78.16±3.42) year and (66.47±5.84) year (P<0.05); the two groups gender composition ratio were 1:8 and 1:1.53(P<0.05); There were 34 cases and 83 cases of Singh index was less than level Ⅲ for the two groups (P<0.05); on 6 related complications (hypertension, diabetes mellitus,cataract, stroke, rheumatoid arthritis, Parkinson's disease)， except the Parkinson's disease,the other 5 diseases associated for the two groups, the difference had statistical significance (P <0.05);Harris score of the contralateral hip for two groups were （95.16±9.57）points and (98.12±4.81)points (P >0.05).  Conclusion Fall is the direct cause of the the second fracture of the contralateral femoral neck after primary femoral neck fracture for aged ,female、increase of age、 BMD decrease and high complication are unfavorable factors With the exception of Joint function decline for the Initial fracture.