Sliders motion error is the key error source of 3-PUU parallel coordinate measuring maching(CMM), which must be corrected or compensated carefully. The influence of sliders motion error on ball hinge centre position and linear grating reading are discussed and evaluated qualitatively, then the error model including slider linear motion error is established, slider motion straightness error data of 3-PUU CMM are captured by dual frequency laser interferometer. Through theoretical calculation, the contribution of sliders motion error on the instrument total error is derived and provided quantitatively with obtained experimental data，which paved the way for error correction. The work will be very useful for the following instrument accuracy calibration. Especially, it will improve the calibration accuracy on the parallel mechanism structure parameters.