The invention discloses a bearing capacity determination method for a concrete filled steel tube lagging jack. The method comprises the following steps: step (1): establishing a mechanical calculation model of the concrete filled steel tube lagging jack, wherein the sections taken from the lagging jack are control sections S and the quantity of the sections S is predetermined as t; step (2): calculating the internal force of the ith control section Si, wherein i is greater than or equal to 1 but less than or equal to t; step (3): judging whether the control section Si of the lagging jack reaches the ultimate bearing capacity or not according to a positively eccentric criterion and a negatively eccentric criterion; and step (4): solving the bearing capacity of the concrete filled steel tube lagging jack, wherein the bearing capacity of the concrete filled steel tube lagging jack is the ultimate bearing capacity of the control section Si firstly emerging on the lagging jack; if the Si reaches the ultimate bearing capacity, the bearing capacity of the concrete filled steel tube lagging jack Qy is Qy=the integral of qyds, and qy is the load on the control section Si.