In this study, we employ the time-resolved optical pump-terahertz probe (OPTP) spectroscopy based on a femtosecond laser system with a central wavelength of 800 nm, pulse duration of 120 fs, and repetition rate of 1 kHz to systematically explore the ultrafast terahertz photoconductive characteristics and terahertz emission properties of topological ferromagnetic Heusler semimetal Co₂MnAl thin films, with conventional ferromagnetic Fe thin films as a reference sample. By introducing magnetic field modulation to fully separate terahertz emission signals from pump-induced transmission signals, and quantitatively analyzing the transient photoconductivity dynamics using the Tinkham thin-film approximation model, we directly observe a distinct photoexcited carrier-driven positive-negative photoconductivity conversion behavior in Co₂MnAl thin films under femtosecond laser excitation. In sharp comparison, Fe thin films only display negative photoconductivity governed by electron-electron scattering, and its relaxation processes show negligible dependence on pump laser fluence. Originating from the characteristic spin-resolved metallic/semiconducting dual band structure in Co₂MnAl, the initial positive photoconductivity within sub-picoseconds is ascribed to the increased population of photogenerated carriers in the minority-spin semiconducting channel, whereas the subsequent ultrafast switching to negative photoconductivity arises from the formation of dynamic polarons that drastically suppress carrier mobility. Furthermore, the photoconductivity peak magnitude of Co₂MnAl can be flexibly modulated by varying pump fluence. The peak-to-peak amplitudes of terahertz emission from both Co₂MnAl and Fe thin films exhibit a linear increase with increasing pump fluence, indicating a similar optical excitation mechanism dominated by magnetic dipole and anomalous Hall effects. This work not only clarifies the intrinsic ultrafast photophysical mechanisms and spin-dependent carrier dynamics in Co₂MnAl thin films, but also realizes the spectroscopic discrimination of majority-spin and minority-spin carrier behaviors, which provides critical experimental evidence and physical insights for optimizing the terahertz radiation performance of cobalt-based Heusler alloys and designing high-performance ultrafast spintronic and terahertz optoelectronic devices.