The invention relates to a tiled grating displacement error monitoring system, which comprises a grating tiling device for mounting a tiled grating, wherein a fine adjuster platform of the grating tiling device is provided with a piezoceramics driver; two polar plates of a first digital capacitance micro-displacement sensor are oppositely arranged on positions in the horizontal direction of a coarse adjuster platform and a lower platform of the fine adjuster respectively; two polar plates of a second digital capacitance micro-displacement sensor are oppositely arranged on positions perpendicular to the lower platform and an upper platform of the fine adjuster respectively; output ends of the first and second digital capacitance micro-displacement sensors are connected with the input end of a signal sample circuit; the output end of the signal sample circuit is connected with the input end of a controller of a singlechip; the output end of the singlechip is connected with a PC through a serial port communication circuit; and the output end of the PC is connected with the control end of the piezoceramics driver through a D/A converter.