The present invention provides a sampling sustaining amplifier which comprises a sampling sustaining circuit and a buffer circuit. The sampling sustaining circuit receives input signal and transmits the input signal to a first node according to the control signal. The buffer circuit is coupled between a power supply source and a grounding end and is controlled by the first node for supplying output signal to the output node. The buffer circuit comprises a primary metal oxide semiconductor transistor. Furthermore the primary metal oxide semiconductor transistor is coupled with the output node.