The invention discloses a method for analyzing nozzle blocking according to heat flow density. The method comprises following steps: obtaining bilateral heat flow density curves of a narrow copper plate in a casting process in real time; determining whether the change rules of the bilateral heat flow density curves are consistent; if the change rules are not consistent, determining that the nozzle is blocked. According to the method, the flow field in the mold was monitored in real time by monitoring the change of heat flux density in a crystallizer so as to avoid changing nozzles when nozzles are already blocked; the method is simple and easy to operate; nozzle blocking can be determined in advance; the technical problem that, in the prior art, the way of judging nozzle blockage according to that the stopper rises to the highest position cannot solve the problem of slight unilateral blockage of the nozzle is solved.