In this work, the support vector machine (SVM) method is adopted to separate BL Lacertae objects (BL Lacs) and flat spectrum radio quasars (FSRQs) in the plots of the photon spectrum index against the photon flux, αph∼logF, those of the photon spectrum index against the variability index, αph∼logVI and those of the variability index against the photon flux, logVI∼logF. Then, we used the dividing lines to distinguish BL Lacs from FSRQs in the blazar candidates of uncertain types from the Fermi/LAT catalogue. Our main conclusions are: 1. We separate BL Lacs and FSRQs by αph=−0.123logF+1.170 in the αph∼logF plot, αph=−0.161logVI+2.594 in the αph∼logVI plot and logVI=0.792logF+9.203 in the logVI∼logF plot. 2. We obtain 932 BL Lac candidates and possible BL Lac candidates, and 585 FSRQ candidates and possible FSRQ candidates. 3. Discussion is given regarding comparisons with the literature.