Installing a circulating water pump is part of the assembly process in power plant construction. This process still needs a human hand; however, the operators faced a high-risk health condition, including posture risks that lead to musculoskeletal disorders (MSDs) and injury. This paper aims to assess the work posture risk of the operator during the installation of a circulating water pump and propose some improvements to increase the safer working environment. By applying NIOSH, Rapid Upper Limb Assessment (RULA), and Rapid Entire Body Assessment (REBA), coupling shaft activity and installing a circulating water pump (CWP) into the well were assessed. The result shows that the process has a 2.33 score for the NIOSH (dangerous posture), a 7 score for RULA (action level 4 is needed), and a grand score of 4 for REBA (need action level 2). The improvement proposed is designing an eye bolt, round clamp, and a holder to help with coupling shaft assembly activities and inserting CWP on the well activities. Those additional tools promote a safer working environment, a better grip, and a better steady posture for the operator, and they reduce work posture risk based on NIOSH, RULA, and REBA scores.