A real-time error measurement system was developed to measure the motion error of a two-dimensional linear module. The system consisted of a four-degree-of-freedom motion error measurement module （for measuring the horizontal straightness， vertical straightness， pitch angle， and yaw angle errors）， roll angle error measurement module （for measuring the roll angle error）， and linear grating ruler （for measuring the axial positioning error）； thus， it measured six degrees of freedom motion errors in a single axis. The principle of the homogeneous transformation matrix （HTM）， was used to construct a spatial error model for the two-dimensional module to represent the actual spatial positions of functional points. The calibration experiments of the measurement system were performed， and the experimental data were processed based on the Abbe-Bryan principle to complete the comparison experiment. Finally， the positioning， straightness， and measurement accuracies of angular errors reach ±1.2 μm， ±1.3 μm， and ±1''， respectively. The measurement error of the diagonal position in the XZ plane of the two-dimensional linear module was analyzed based on the proposed spatial error model. The results indicate that the measurement error of the diagonal position in the XZ plane decreases from 68 μm to 13 μm after using the two-dimensional linear module spatial error model. In addition， because the motion errors of the two-dimensional linear module at different positions changes under loading， a comparative experiment was conducted by adding a standard weight of 2 kg to the Z-axis slider to verify the measurement system could capture real-time spatial error variations of the linear module. The results show that the measurement error of the diagonal position in the XZ plane decreases from 56 μm to 14 μm after using the two-dimensional linear module spatial error model.