Abstract: The effective length factor is a crucial parameter for calculating the stability of members, and how to determine the effective length factor is an important issue in the design of single-layer latticed shells. Based on the structural elastic stability theory, this article derives the formula for calculating the out-of-plane effective length factors for semi-rigid joint single-layer latticed shell members and establishes the relationship between the effective length factors and the rotational stiffness of joints. Finite element buckling analyses are performed on single-layer latticed shells with varying characteristics, including shell types, member positions, member sections, rise-span ratios and rotational stiffness of joints. The effective length factors are determined based on the local buckling capacities of members and Euler’s formula, and the relationships between the effective length factors and various parameters are obtained. By combining theoretical and numerical results, both the relationship curve and the fitting formula for the effective length amplification factor and the rotational stiffness of joint are established. Subsequently, a practical calculation formula for the out-of-plane effective length factor of members of single-layer lattice shell with semi-rigid joints is proposed according to the specifications.