Focused on the issue that elderly can be rescued timely after falling down, a fall detection device for the elderly based on acceleration vector feature is designed. The device combined with the accelerometer sensor MMA8452Q、GSM communication and GPS positioning technology, by analyzing the characteristics of acceleration vector when the body posture changed, used the Z axis component of the acceleration and acceleration amplitude as the basic standards to determine fall accident. Furthermore, considering whether it is serious or not after the fall, we also use the instantaneous change of acceleration amplitude as the assistant criterion to improve the accuracy of judgment of fall detection. According to above criterion, the device can alarmed and sent the elderly location information for rescuing in time. The experiment results show that the device can accurately distinguish between the elderly's daily behavior and the state of falling down in which need helping. When the accidentally falls happen ,it can send an alarm in the first time , reduce the risk of fall and has strong practicability.