The discrete-time amplifier has the property of sample and hold, thus it is difficult to adopt local feedback method to deal with offset and flicker noise. A calibration-free swap-combine noise cancellation technique is proposed to remove the input-pair-introduced mismatch in discrete-time amplifiers with keeping the same external interface so it can directly replace the original amplifier. The proposed method can eliminate the flicker noise by modifying the noise transfer function, as well as achieve significant offset suppression. Simulation of a prototype shows that it can reduce the offset root mean square from 10mV to 0.25mV. Benefiting from avoiding calibration loops, the proposed method can also deal with input common-mode voltage variation and temperature drift, as well as reducing the calibration area cost and initial delay.