In order to reveal the distortion mechanism of PLA thin-plate part in the FDM process, a theoretical model based on the theory of elastic thin plates in thermoelasticity was established, and an experimental research approach based on Taguchi method was presented. A special specimen was designed, and the flowchart of experimental procedure was elaborated. Moreover, 81 test specimens were prepared through FDM process and measured by a portable 3D laser scanner. Two statistical analysis methods, signal to noise ratio (S/N) and analysis of variance (ANOVA), were applied to optimize the process parameters in order to reduce the distortion of thin-plate part. The experimental results indicated that the optimal process parameters can be obtained and proposed theoretical model was proved efficient.