The present invention disclosed an automated prosthetic arm for amputees consists of a 3D printed prosthetic arm; servo motors constructed inside the 3D printed prosthetic arm; a stretch sensor harness; a stretch sensor constructed inside the stretch sensor harness; an arduino microcontroller; and a power supply circuit. Besides, the present invention also disclosed a method to control an automated prosthetic arm comprising the steps of: constructing and assembling the stretch sensor into the stretch sensor harness; wearing the stretch sensor constructed inside the strecth sensor harness onto the shoulder of the amputees; detecting the shoulder stretch action of the amputees and converting the shoulder streching action into the electrical signal by using the strech sensor; processing the electrical signal provided by the strech sensor into pulse width modulation (PWM) signal by using an arduino microcontroller; and sending the PWM signals to the servo motors for controlling the grips of the hand region of the 3D printed prosthetic arm.