The propagation of intense femtosecond laser pulses in air involves many linear and nonlinear effects, such as diffraction, dispersion, Kerr self-focusing, multiphoton ionization, etc. When the Kerr self-focusing effect and the plasma defocusing effect reach a dynamic equilibrium, a high-intensity "optical filament" is generated. The properties of filamentation have attracted significant attention owing to many interesting phenomena, such as conical emission, third-order harmonic generation, and supercontinuum (SC) radiation. Specifically, the SC spectra induced by filaments undergo a significant extension covering a wide range from the UV to the mid-IR and attracts considerable interest for its potential application in remote sensing detection of atmospheric pollution. Therefore, it is of great significance to explore the propagation of filament and the characteristics of mid-infrared spectral in complex atmospheric environments.Based on the (3D+1) dimensional nonlinear Schrödinger (NLS) equation, the transmission characteristics of femtosecond pulses in air are described. Firstly, under the slowly varying envelope approximation, we use the evolution of the cylindrically symmetric linearly polarized laser electric field along the propagation axis z to describe the propagation dynamics of femtosecond laser pulses in air. Secondly, the time Fourier transform and the spatial Crank-Nicholson difference scheme are used to numerically solve the coupling equation. Finally, by adjusting the laser pulse input parameters (such as input power, waist width and pulse width) and the focal length of the lens, the filaments are generated by intense femtosecond laser pulses at different heights within 1 km from the ground.In this paper, using atmospheric stratification model and numerically analyzing that pressure, beam waist width, pulse width and attenuation of scattering medium influence on the transmission of the filamentation and the characteristics of supercontinuum spectrum. The results show that: Small changes in pressure lead to significant changes in the characteristics of optical filaments (starting position, length, stability, energy flux, and axial intensity time distribution), which directly affect the characteristics of the supercontinuum spectrum excited by plasma filaments; With the increase of waist width and pulse width, the starting point of the filaments is closer and closer to the ground. Then, by analyzing the intensity spectra, the effects of beam waist width and pulse width on mid-infrared spectra are further discussed. It is found that the mid-infrared spectral intensity decreases with the increase of beam waist width under the same focal length. As the filaments are produced farther from the ground, the intensity of the mid-infrared spectrum becomes stronger. At the same time, the spectrum excited by plasma filaments can cover the whole wavelength range of visible light, and the redshift wavelength can extend to 5 μm; Although the scattering medium causes exponential attenuation of laser energy, especially when the laser beam reaches an altitude of about 500 m, this attenuation has a more significant effect on the characteristics of the optical filaments. However, with appropriate initial parameters, the attenuation has a minimal impact on the mid-infrared spectrum intensity within the supercontinuum spectrum. Therefore, it is extremely important to regulate these parameters, and this study provides an important theoretical basis for detecting the composition of atmospheric pollutants by using mid-infrared spectroscopy at different altitudes in the upper air.