Abstract. SAR ADC is the best choice for low-power and high-resolution application in signal processing systems, since it is fit to work in midst rate per conversion (MSPS, GSPS). In order to guide trade-off design better, this paper starts with analyzing the advantages and disadvantages of known FoMs (figure of merits) of traditional SAR ADC. To keep the characteristic of minimum merit values and grasp the feature of bright distinctive degrees, one novel FoM of SAR ADC was built with five key parameters. Total four kinds of FoMs were compared with convinced data from 15 pieces latest literatures, including Q (based on 2-parameter), FoM 0 (based on 3-parameter), and FoM 4 (based on 2-parameter). As interesting results, the compromised design parameters region had gained. This work may provide SAR ADC designers one new practical evaluation function for efficient optimization design future.