Abstract: The detection of the filed-aligned currents is an important scientific subject for the Europe Incoherent SCATter radar association (EISCAT). Using the different channels, the ion line and the plasma line can be observed synchronously by the incoherent scatter radar, which can be used to deduce the resonance frequency of the ions and electrons, and the filed-aligned current can be determined by these frequencies. The method is reasonable for the plasma with the Maxwellian distribution. However, the heat flow can be caused by the drift velocity in the velocity phase space. The 16-moment distribution function is used to describe the heat flow effect. On this basis, the solutions of the dielectric function and dispersion relation with a complex frequency are presented for an arbitrary velocity distribution, and the results are compared with those of Maxwellian distribution. The effects of the heating flow on the electron velocity distribution function, the real and imaginary parts of dielectric function, the resonance frequency and damping rate of ions and electrons, are discussed. With a positive electron drift velocity, the filed-aligned currents will be overestimated by the measurement of upshifted plasma line, and with a minus electron drift velocity, the filed-aligned currents will be underestimated. For the case that both upshifted and downshifted plasma lines are measured, the filed-aligned currents will be overestimated.