The invention discloses a biological soil conditioner for reducing soil acidity and a preparation process thereof and relates to the technical field of agriculture. Bacterial cellulose is oxidized first and then mixed with collagen and nano-based bentonite for a reaction to obtain a composite material; the composite material is freeze-dried after a reaction and then reacts with a modifier to obtain modifier-treated porous microspheres; then the modifier-treated porous microspheres are mixed with modified sodium lignosulfonate cultured by mixed bacteria, the mixture is stirred in a 90% ethanolsolution for a reaction and then filtered and dried, and potassium humate is added into the mixture to obtain the biomass conditioner. The biomass conditioner prepared by means of the process can effectively adjust the pH of acidic soil and has an excellent adsorption effect on metal ions.