In order to carry out the experimental study of laser plasma instability (LPI) on the laser device cluster platform with an output energy of 100kJ, a scattered light diagnosis system based on cluster configuration is built. The diagnosis system uses the diffuse reflector as the main light blocking, reflection, and sampling element, the imaging method is used to image the scattered light to the recording components such as iCCD (intensifier Charge Coupled Device) camera, and the sampling measurement method is used to obtain the spatial distribution, energy, spectrum, and time waveform of the scattered light. In the cluster physics experiment, the physical data obtained by the system are in good agreement with the results obtained by the physical simulation program. It shows that the scattering mechanism is mainly subbeam mechanism under the current conditions, and its action process mainly concentrates on the early stage before the plasma empties.