The invention provides a temperature distribution measuring method of a shielded nuclear main pump cooling system. The method comprises the following steps: establishing an equivalent physical model of the shielded nuclear main pump cooling system, and setting the devices on an upper cooling loop and a lower cooling loop as nodes; obtaining the mass flow rate, equivalent heat effect power and specific heat of the cooling liquid at each node; determining the temperature changes of corresponding nodes; obtaining the flow before the confluence of two branches at each confluence point and the flow after confluence, and determining the temperature change relation at the confluence points according to energy conservation; and selecting one point in the loop as a temperature start point, and serially connecting the temperature changes according to a topological structure to obtain the temperature distribution of the equivalent physical model. By adopting the method provided by the invention, the overall temperature distribution of the shielded nuclear main pump cooling system can be obtained to facilitate system analysis.