The low-power consumption and low-noise sensor remain an important challenge in Electrocardiogram (ECG) sensor field. A new operational amplifier (op-amp) design is proposed in this study, and it is integrated into the traditional "right-leg-drive"circuit to cancel out the common-mode interference. Besides, the gain of this circuit can be controlled by adjusting the value of these resistors. Then, the traditional op-amp is redesigned to improve the performance of this circuit. Some improvements are made on the basis of the traditional sleeve-type cascade amplifier to obtain good gain and gain bandwidth. At the same time, power consumption is not too high. Meanwhile, to minimize the noise of the op-amp without using large value capacitors, pseudo-resistors are used. The right-leg-drive circuit is used in the overall process to ensure good common-mode rejection ratio (CMRR) performance. For the newly designed op-amp, its gain can reach 60db, and the operating frequency of the circuit is between 0.1HZ and 108HZ, and the error is no more than 10%. The differential mode gain of the overall circuit is 43.4db, and the error is within 5db. The total power consumption of the circuit is 3.17u watts, which is less than the specified maximum power consumption, and the total integrated input-referred noise is 3.786μVRMS, which is less than the specified maximum circuit noise. The total capacitor usage is 1nF, less than the specified maximum capacitor usage. To sum up, the ECG sensor is designed using the "right leg drive circuit"and a new type of amplifier is designed to eliminate common-mode interference and improve the performance of the amplifier.