The present invention provides a method for efficiently preparing 2,3,3,3-tetrafluoropropene (HFO-1234yf) by a simple and economically advantageous method that is suitable for implementation on an industrial scale. The present invention provides a process for preparing 2,3,3,3-tetrafluoropropene, comprising the step of: (1) in a reactor, (1-1) reacting 1,1,1,2,3-penta-chloropropane with hydrogen fluoride in an amount of 10 to 100 mol per mole of the 1,1,1,2,3-pentachloropropane 1; (1-2) in the presence of chromic oxide represented by composition formula: CrOm (1.5