The analytic expressions of lightning electromagnetic fields generated by tortuous channel with an inclined lower section are obtained by decomposing the current infinitesimal and solving Maxwell's equations. By using the transmission line model and pulse function to express the channel-base current, the influence of length and tilt angle of the oblique part on lightning electromagnetic fields as well as the distribution laws of electromagnetic fields for different azimuth angles are analyzed. The results show that the electromagnetic fields in near area are mainly determined by the lower section of the tortuous discharge channel, and the peak values of electromagnetic fields in different field regions will increase with the increasing of the length of the lower section when L1 is shorter than the distance that return-stroke speed multiplied by peak time. Whereas the length of the lower section is longer than the distance that return-stroke speed multiplied by peak time, the waveforms of electromagnetic fields will overlap each other and won't be influenced by oblique part length of the discharge channel before the return-stroke current arrives at the inflection point. Moreover, the peak values of electromagnetic fields will decrease with the increase of tilt angle (the azimuth angle φ = 2π/3) and azimuth angle, and the impact of channel geometry on the electromagnetic field strengthens with the distance.