A portable test instrument for a rivet nut setting tool is disclosed, and the portable test instrument includes a shell body, a circuit module disposed in the shell body, and a strain gauge having a part located in the shell body and electrically connected to the circuit module, and a display device. An end of the strain gauge is exposed to the shell body and used to mount with the rivet nut setting tool. The strain gauge can change a value of a signal transmitted to the circuit module when being forced to deform. The display device is disposed on the shell body and electrically connected to the circuit module, and configured to display data measured by the strain gauge.