The ECG monitor can continuously record the ECG data for a long time, so it has been an indispensable medical instrument in hospital wards. And now it is more and more popular in the family. An ECG monitor is designed and implemented based on ARM microprocessor in this thesis. AD8232 is used as the ECG frontend acquisition chip to obtain the ECG signal, and the signal is filtered and denoised after being amplified by amplifier and filter circuit. The ECG signal is converted from analog to digital using the STM32 microprocessor as signal processing chip and sent to the smart terminal through the Bluetooth module ATKHC05. Then electrocardiogram can be drawn and display in real time in the smart terminal. In the design of the system, the detection of lead drop and the realization of low power consumption mode are fully considered, so the ECG monitor will be widely used in the market because of its accurate data, light weight and so on.