The invention discloses an internally-cooled piston with a detachable oil cavity inner core. The piston comprises a piston main body, the inner core and a quartz glass top surface, wherein quartz glass top surface fixing bolts, inner core fixing grooves, an inner core accommodating cavity and a quartz glass top surface accommodating table are arranged at the top of the piston main body; the inner core fixing grooves are formed in the two sides of the inner core accommodating cavity; an oil inlet channel and an oil outlet channel are formed in the piston main body and communicated with the inner core accommodating cavity respectively. A model can be used for related testing of the influence of different oil cavity shapes on oscillation flow heat transfer of the piston, the inner core is fixed to the upper part of the main body model before testing, and the flowing properties of fluids in cavity bodies can be shot through a transparent quartz glass plate on the top surface; by replacing the inner core, the flowing properties of the fluids in the different cavity body shapes can be obtained; through comparison and research, the influence of the different cavity body shapes on the flowing can be obtained; a support is provided for optimized design and application of the internally-cooled piston.