In this paper, the electrical conductivities of ionic liquid 1-butyl-3-methylimidazolium bis [(trifluoromethyl)sulfonyl]imide ([BMIM][TFSI]) in mixed organic solvents of propylene carbonate (PC) + gamma-butyrolactone (GBL) and ethylene carbonate (EC) + dimethyl carbonate (DMC) were measured. The effects of mixed organic solvents with different ratios (1:0, 2:1, 1:1, 1:2, 0:1) on the electrical conductivity of ionic liquid were investigated. The organic solvents EC and DMC have a synergistic effect for the electrical conductivity of [BMIM][TFSI]-EC/DMC, and the optimal ratio of EC to DMC is 1:1; however, the organic solvents have no synergistic effect in [BMIM][TFSI]-PC/GBL. The concentration dependence of the electrical conductivity of the solution can be well fitted by the empirical Casteel-Amis equation. The effects of temperature on electrical conductivity can be described by the Vogel-Tamman-Fulcher (VTF) equation and the Arrhenius equation. The IL concentration dependence of the activation energy E-a and the pre-exponential factor A in the Arrhenius equation were also investigated, and fitted by empirical equations. On the basis of the VTF equation and the Arrhenius equation, a quasi-Arrhenius equation was proposed to describe the effects of temperature and composition on the electrical conductivity simultaneously in binary systems and ternary systems, and the correlation results agree well with the experimental results.