We present a study of the LAMOST spectra and public photometric data for four AM CVn binaries with orbital periods ranging from 17 to 41 min. The prototypical star AM CVn displays short-term brightness fluctuations, which most likely arise from its superhump modulation. The superhump period of PTF1J0719+4858 is identified to be 1659.85(13) s, slightly longer than its orbital period. We find a short-lived dip in the phase-folded light curve centered on a phase of similar to 0.5 during the 2008 March outburst of YZ LMi. This dip can be interpreted as the obscuration of the accretion flow or inner disc. The superhump period of V493 Gem has a positive period derivative during the middle stage, which can be seen in most SU UMa-type cataclysmic variables (CVs). By applying the growing superhump method we determined its mass ratio to be q = 0.0315(24). The quiescent spectra of both PTF1J0719+4858 and V493 Gem show clear metal lines and reveal a possible white dwarf donor. We also discussed the theoretical values of the donor mass and the mass transfer rate of these two systems.