This study provides details of a novel continuous process to eliminate the pollution of yellow phosphorus tail gas, which can also produce high quality and low cost formic acid, with a particular focus on the high and variable viscosity of the system and the rationality of energy utilization. A compact acidification reactor was developed as the key equipment used in this novel process, based on integrating the reaction, heating and condensation reflux. In addition, the effects of the mole ratio of the reactants, formic acid additive content, reaction time, reaction temperature and agitation speed on product concentration and yield were also researched experimentally. The experimental results show that as the mole ratio of the reagent increases, the product yield rises significantly while the concentration only increases slightly. The concentration and yield of the product decrease if less formic acid additive is added to the system. As the reaction time increases, both the concentration and yield of formic acid are increased, especially when the reaction time is over two hours. The reaction temperature has little effect on the product concentration, whereas the product yield would increase first and then decrease as the reacting temperature increases. The effects of agitation speed on the concentration of formic acid are not significant.