A tunnel constructing method involves a formwork, a driving device, a supporting block, a connecting rod, a walking system, a base, a main bridge, a square platform, a supporting column, a working platform, a traction claw, a traction rod, a traction wheel, a storage type platform frame, a storage type fence, a front bridge, a slope, a rear bridge, a traction rope bayonet and a concrete plate. Theconstructing method includes the lining method, the concrete pouring method and the nozzle switching method. The lining method includes the steps of arranging steps on the square platform so that anoperator can climb up the square platform through the steps, rotating the storage type platform frame so that the storage type platform frame can be unfolded to get close to the formwork, conducting pouring lining through a pouring hole in the formwork by the operator, conducting lining automatically through the pouring hole in the formwork by means of a pouring pipeline in a pipeline groove, andgiving an alarm to remind the operator of the ending of the pouring when a sensor senses the ending of the pouring.