  Very high energy (VHE; $E \geq$ 100GeV) $\gamma-$ray from cosmological
distances are attenuated by the extragalactic background light (EBL) in the IR
to UV band. By contrasting measured versus intrinsic emission, the EBL photon
density can be derived. However, neither the intrinsic spectra nor the EBL is
separately known~-~except their combined effect. Here we first present a
flexible model-dependent optical depth method to study EBL by fitting the
emission spectra of TeV BL Lacs objects via a one-zone leptonic synchrotron
self-Compton model (SSC). We have little information about electron energy
distributions (EEDs) in the jet, which is critically important to build
spectral energy distributions (SEDs) in SSC scenario. Based on the current
particle acceleration models, we use two types of EEDs, i,e., a power-law
log-parabola (PLLP) EED and a broken power-law (BPL) EED to fit the observed
spectra. We obtain that the upper limits of EBL density are around about 30 n W
m$^{-2}$ sr$^{-1}$, which are similar to the published measurement.
Furthermore, we propose an unprecedented method to test radiation mechanisms
involved in TeV objects by simply comparing the reduced EBL density with the
limit obtained by galaxy counts, and demonstrate that for some BL Lacs, at
least, the one-zone SSC model should be reconsidered.
