The present invention relates to a process for producing 1,1,1,2-tetrafluoroethane by gas-liquid phase method, taking trichlorethylene and hydrogen fluoride as raw materials, comprising the steps of: trichlorethylene and hydrogen fluoride generating F133a under the action of a fluorination catalyst, hydrogen chloride, F123 and F131, potassium hydroxide solution and hydrogen fluoride to produce potassium fluoride, potassium fluoride and F133a in the role of fluoride catalyst, the control temperature of 250-280 ℃, the finished product 1,1,1,2-four fluoroethane, the reaction conversion rate of up to 80%. The hydrogenation of the raw materials of the invention and the hydrogen chloride generated in the reaction process are small, and the corrosion of the reaction is far less than that of the hydrogen fluoride, and the investment of the equipment is little.