The present invention discloses a testing device for monitoring a flow field and interlay stress of an oil depot in a cavity construction period, which comprises a layered rock salt cavity construction model, a PIV (peak inverse voltage) detection system, a stress and strain analyzer and a tracing device. The layered rock salt cavity construction model comprises a U-shaped rock salt module, a steel plate arranged on the inner wall of the rock salt module, a double-layer sleeve and two pieces of organic glass; the U-shaped rock salt module is clamped between the two pieces of organic glass; the double-layer sleeve is inserted into a cavity and is respectively connected with a water injection pipe and a halogen discharging pipe, and the tracing device is arranged on the water injection pipe; a laser transmitter in the PIV detection system transmits light into the cavity, and a camera monitors changes of the flow field; and a stress gauge is arranged on the steel plate, and the signal output end of the stress gauge is connected with the stress and strain analyzer. The testing device can analyze the migration law of the flow field in the cavity construction period more accurately and qualitatively, realize the dynamic monitoring of the rule of changes of the interlayer stress during cavity construction, and reflect the rule of interaction of the flow filed and the interlayer during the whole cavity construction process.