The invention provides a mechanical seal device for a nuclear power station reactor coolant pump. The mechanical seal device is formed by connecting three stages of mechanical seals the same in structure in series in a press-fitting manner. Each mechanical seal comprises a seal assembly, a shaft sleeve, a cavity and a spring seat. Each seal assembly comprises a moving ring, a fixed ring, a movingring seat connected with the moving ring, a fixed ring seat connected with the fixed ring, a moving ring clamp ring and a fixed ring clamp ring. A spiral pump efficiency structure is arranged on the outer side face of each moving ring clamp ring. According to the mechanical seal device, the flowing condition of media nearby the seal assemblies is improved, temperature increase of the seal assemblies is prevented from being too large, wear of a seal end face is reduced, and the service life is prolonged.