The invention discloses a five-degree-of-freedom error synchronous measurement device and method for a linear motion system; the device comprises a fixed emission unit, a movement measurement unit anda signal processing unit; optical signals detected by four two-dimensional PSD position-sensitive sensors are connected with an upper computer through a USB after passing through a signal processingcircuit, an inclination angle sensor is in communication with the upper computer through the Bluetooth, and the straightness of the horizontal direction, the straightness of the vertical direction, the pitching angle, the deflection angle and the roll angle error of the linear motion system can be obtained by decoupling through processing of a measurement analysis module. According to a strict position relation design, the influence of optical element assembly errors on the measurement result can be ignored. All the measurement data are directly measured by the sensor instead of being obtainedthrough indirect calculation by establishing a complex mathematical model, so that the error caused by using complex mathematical calculation is reduced.