A　portable　spectrometer　prototype　is　built　to　study　wavelength　calibration　for　flat-field　grating　spectrometers.　An　accurate　calibration　method　called　parameter　fitting　is　presented.　Both　optical　and　structural　parameters　of　the　spectrometer　are　included　in　the　wavelength　calibration　model,　which　accurately　describes　the　relationship　between　wavelength　and　pixel　position.　Along　with　higher　calibration　accuracy,　the　proposed　calibration　method　can　provide　information　about　errors　in　the　installation　of　the　optical　components,　which　will　be　helpful　for　spectrometer　alignment.