After　a　DC-accuracy　of　0.04%　was　obtained　on　a　low　cost　10-Msample/s　(Msps)　13-bit　A/D　converter,　the　dynamic　accuracy　was　investigated　by　means　of　the　effective　number　of　bits　(ENOB),　FFT　analysis　and　the　error-amplitude　of　the　spurious　data.　The　improvement　of　dynamic　accuracy　is　made　by　using　hardware　method.　and　software　method.　Experiments　showed　that　the　gain-bandwidth　of　the　operational　amplifier　subtracting　the　high-3-bit　D/A　output　voltage　from　the　A/D　input　voltage　is　the　key　of.　the　hardware　method.　Experiments　showed　that　FFT　filter　smoothing　is　on　effective　software　method　for　improvement　of　dynamic　accuracy.　However,　the　number　of　points　set　for　FFT　filter　smoothing　is　crucial.　Larger　number　of　the　FFT　filtering　points　makes　reduction　of　the　amplitude　of　the　smoothed　data　of　sine　wave.　This　makes　the　improvement　of　dynamic　accuracy　by　FFT　filter　smoothing　vary　limited.