Corner-tube boiler is widely used in the production of industrial steam. For this boiler, it is difficult to conduct hydrodynamic calculation and check due to unique water cycle structure. A new method for hydrodynamic calculation of corner-tube steam boiler based on differential pressure solution is proposed in this article. The frictional pressure drop in the lower header has been taken into consideration by adding a direction discriminant factor, which can solve the inherent problem about the balance point. Meanwhile, taking a corner-tube steam boiler of 75 tonne per hour as an example, the circulation flow rates in each riser under different working conditions were calculated, and the cycle reliability was also checked. The calculation results showed that the hydrodynamic characteristic is good enough under the condition of full heat load. However, the riser in the tail shaft will surf from flow stagnation or backflow once the heat load is at or below 50%, which is generally consistent with the change trend of monitoring wall temperature during actual operation. This method proposed in this article is more accurate, by comparing with the traditional method, in predicting whether there is a risk of flow stagnation or backflow in the riser of the corner-tube steam boiler under lower heat load.