The invention provides a detection method of gas reaction concentration and a detection device and belongs to the technical field of concentration detection. The detection method is characterized by comprising the following steps: step 1), measuring total volume flows Q1 and Q2 of gas reactants before reaction in real time; step 2), calculating a real-time volume flow difference delta Q of gas before and after a chemical reaction; step 3), determining a relation between a volume change value delta V and a volume V of gas to be detected of the gas before and after the reaction and calculating avolume flow Q3 of the gas to be detected; step 4), equalizing each gas reactant into an equivalent reactant according to a ratio of corresponding stoichiometric numbers; step 5), calculating the gasmass percent of the gas to be detected. According to the detection method of the gas reaction concentration, through gas volume change relation before and after the chemical reaction, the difficulty in the prior art that the gas needs to be detected through a sampling manner is overcome, and the detection accuracy and the detection stability are improved; an ozone generation device can be used formonitoring the concentration of produced ozone in real time.