The invention discloses a thermal power generating unit zero-power protection system and method. When a power plant sending-out circuit suffers from a failure to result in control valve rapid-closing action or unit power oscillation, and if zero-power protection criterion is not perfect, zero-power protection suffers from misoperation. The thermal power generating unit zero-power protection system comprises a starting criterion module, an action criterion module and an outlet logic module, wherein the starting criterion module comprises an electrical sudden change amount criterion and a zero-power protection putting-in-use criterion; the electrical sudden change amount criterion and the zero-power protection putting-in-use criterion form AND gate logic; the electrical sudden change amount criterion is the main criterion in the starting criterion and consists of generator voltage sudden increasing, current sudden drop, and power sudden drop; and the outlet logic module comprises an outlet judgment logic, self-holding logic and outlet time delay. By virtue of the thermal power generating unit zero-power protection system and method, generator zero-power protection operation reliability is improved.