During the LPBF (Laser Powder Bed Fusion) process, excessive residual stress can lead to a decline in the forming quality of printed parts. Residual stress is the primary cause of part deformation; therefore, monitoring the part deformation trend can, to a certain extent, reflect the overall residual stress level of the part. Online stress or deformation monitoring presents significant challenges due to the part being covered by powder and the need for a sealed environment. This paper proposes a novel monitoring system that replaces the bolts used to fix the baseplate with bolts capable of measuring tensile force. The deformation trend of the part will be inhibited by the bolts fixing it to the base plate, and the magnitude of the bolt tensile force is indicative of the magnitude of the deformation trend. Printing experiments were conducted under different scanning strategies and preheating conditions. The experimental curves reveal the patterns of deformation trend evolution in the parts, and these patterns are well explained by existing theories, which confirms the reliability and accuracy of the monitoring system.