A narrow body doublecylinder S valve concrete pump is designed so as to solve the disturbance problem between construction machinery and concrete pump used in singletrack railway tunnel with small crosssection and narrow gallery. The concrete pumping cylinder driven by hydraulic cylinder and the principle of reciprocating mode of double cylinder are adopted for the system; therefore, the width of the pumping system can be reduced to 1.49 m without lowering the pumping capacity. And then, the mechanical properties of major critical components and fatigue life of S valve of the concrete pump are analyzed by software Ansys. The study results show that: 1) The maximum equivalent stresses of piston rod, main cylinder and concrete pumping cylinder are less than yield limits of materials under the action of static load. 2) The maximum equivalent stress of S valve is less than yield limit of material under the action of dynamic load; and the fatigue life of S valve is 50% to 90% of the fatigue sensitive curve, which can meet the requirements of structural strength and fatigue life.