The invention discloses a differential amplification circuit, which comprises two differential amplifier branches, wherein two NMOS (N-channel metal oxide semiconductor) transistors are connected in series to form each differential amplifier branch; one of the NMOS transistors is provided with a thick gate oxide layer and is connected with the side close to supply voltage to determine the working voltage of the circuit; the other NMOS transistor is provided with a thin gate oxide layer but has high threshold voltage; the amplifying performance of the whole circuit is determined by the two NMOS transistors with high threshold voltage, and since the gate oxide layers of the two NMOS transistors are relatively thin, the mismatch between the two differential amplifier branches can be reduced. The differential amplifier circuit disclosed by the invention can carry out regulation separately for the requirement on working voltage and the requirement on mismatch, and has high working voltage and low mismatch; meanwhile, the implementation of the invention only requires a NMOS transistor to be added in each differential amplifier branch, the circuit is simple, the circuit area is relatively small, and the cost is relatively low. The invention also discloses an operational amplifier.