Recent research on parity-time- (𝒫𝒯-) symmetric optical structures have exhibited great potential for achieving distinctive optical behaviour which is unattainable with ordinary optical systems. Here we propose a 𝒫𝒯-symmetric cavity-magnon system consisting of active cavity mode strongly interacting with magnon to study magnon-induced transparency (MIT) and amplification (MIA) by exploiting recent microwave-cavity-engineered ferromagnetic magnons. We find that (i) due to the gain-induced enhancement of coherent coupling between the cavity field and the magnon, the transmitted probe power is remarkably enhanced about four orders of magnitude and the bandwidth also becomes much narrower, compared to passive cavity system. (ii) More importantly, the light transmission can be well controlled by adjusting the applied magnetic field without changing other parameters, and a Lorentzian-like spectra can be established between the transmitted probe power and the external magnetic field, which provides an additional degree of freedom to realize the coherent manipulation of optical transparency and amplification. Our results may offer an approach to make a low-power magnetic-field-controlled optical amplifier in 𝒫𝒯-symmetric cavity-magnon system.