Wearable electrocardiogram (ECG) sensors is a simple test that can be used to check people’s heart's rhythm and electrical activity. With individuals’ increasing attention to their own health, developing a timely and portable bio-sensing recorder has become an urgent task. This paper presents the working principle of a common ECG signal recorder. A double-electrode voltage amplifier that can be used for portable ECG sensors has been set out to design. The amplifier is mainly composed of a differential amplifier circuit, which can lower power supply and power consumption. CoolSpice environment was utilized to simulate the circuit and analyze the result. The simulation presented that the common-mode gain is under 30dB up to 5KHz and the differential-mode gain is larger than 40 dB up to 5KHz. And the total current consumption has been under 20uA. The result demonstrated that the amplifier can perform well. The noise from human body has been eliminated by the amplifier. The amplifier has the ability to extract and amplify clean ECG signals and its structure has the characteristics of low cost and portability. It may be used in portable wearable ECG sensor technology.