The present invention discloses an oudoor field RCS measurement method, which comprises the steps of acquiring at least one group of echo signals, wherein any group of echo signals comprises a target intermediate-frequency (IF) echo signal and a scaling body IF echo signal; for any group of echo signals, conducting the analog-to-digital conversion on the target IF echo signal in the above group of echo signals to generate a first digital signal, conducting the analog-to-digital conversion on the scaling body IF echo signal in the above group of echo signals to generate a second digital signal; conducting the fast Fourier transformation on the first digital signal to obtain a first complex-quantity signal, obtaining a first electric field strength in accordance with the first complex-quantity signal; conducting the fast Fourier transformation on the second digital signal to obtain a second complex-quantity signal, obtaining a second electric field strength in accordance with the second complex-quantity signal; calculating a candidate RCS according to the first electric field strength and the second electric field strength; on the condition that only one group of echo signals is acquired, adopting the candidate RCS as a target RCS. According to the technical scheme of the invention, the phase noise and the attenuation in the oudoor field RCS, caused by the external interference, can be eliminated, so that the RCS measurement error is reduced.