An evaluation method of residual stress in water jet peening includes a step of creating an analytical model including meshes according to a water jet peening (WJP) object, the shape of a nozzle, and an injection distance, a step of inputting WJP execution conditions, a step of calculating the internal pressure pBi of a cavitation bubble and a bubble number density ngi through jet flow analysis for a jet flow jetting from the nozzle, a step of calculating cavitation energy according to the internal pressure pBi of a cavitation bubble and a bubble number density ngi (S4), a step of calculating the burst energy of cavitation bubbles from the cavitation energy C, and a step of calculating the compressive residual stress of the WJP object from the collapse pressure of cavitation bubbles. Accordingly, the residual stress of the WJP object can be evaluated precisely in a shorter time.