Abstract: The detection efficiency calibration of Si(Li) detector in low-energy region down to 1 keV was carried out by measuring the bremsstrahlung spectrum of thick-carbon-target bombarded by 19 keV electron beam. The coupled electron-photon transport Monte-Carlo computer code PENELOPE was employed for theoretical calculation of thick-carbo-target bremsstrahlung spectrum. The absolute value of the efficiency calibration was determined from the use of 241Am radioactive standard source. The uncertainty for the efficiency calibration with present method is mainly stemmed from the use of 241Am radioactive standard source and it was estimated to be about 5%. The preliminary experimental efficiency calibration values were also compared with calculation values based on a simple model. The detector thickness parameters were also determined by a nonlinear least squares fit. Except the Au-contact layer, the other thickness parameters are in acceptable agreement with that provided by detector manufacturer.