Abstract. This paper investigates the method of assembly precision reliability assessment for industrial sensing devices. The part variation is formulated by small displacement torsor. The assembly error model is developed through the approach of pose transformation matrix, then the error transfer between the parts is analyzed and the assembly error is calculated. The concept of assembly precision reliability is proposed. Monte Carlo simulation is adopted to calculate the reliability, after that the procedure of assembly precision reliability is determined. Case study of a laser sensor is provided therefore the effectiveness of the proposed models is verified.