The invention discloses a multi-grade 
waste heat energy 
cascade recycling 
system for a 
diesel engine, and particularly relates to a combined-type 
diesel engine waste heat energy recycling system. The 
waste heat energy recycling system is structurally characterized in that a high-temperature 
Rankine cycle system is composed of a working medium pump, a 
thermoelectric generator, an EGR 
heat exchanger, an 
exhaust heat exchanger, a 
steam turbine, a condenser and the like of a high-temperature system; a low-temperature 
Rankine cycle system is composed of a working medium pump, an EGR 
heat exchanger, an 
exhaust heat exchanger, the cylinder 
body cooling water 
heat exchanger, the supercharged air heat exchanger, a 
steam turbine, a condenser and the like of a low-temperature system. A middle electrical 
machine is arranged between a 
turbine motor and a 
supercharger; the waste heat of cooling water, supercharged air, exhausted gas, EGR recirculated 
waste gas and the like are utilized, and through the high-temperature and low-temperature organic Rankine cycles, thermoelectric power generation, 
turbine direct power generation and the like, heat exchange can be carried out between various kinds of waste heat generated by the 
diesel engine and working media sequentially according to the grade. Due to arrangement of the middle electrical 
machine, the 
expansion ratio of the exhausted gas can be improved, and excess pressure energy of the exhausted gas can be directly recycled. Full recycling of multi-grade waste 
heat energy of an 
internal combustion engine can be achieved, irreversible losses of the system are reduced, the fuel economical efficiency is effectively improved, and therefore the aims of saving energy and reducing emissions are achieved.