To address the issues that the illumination effect evaluation elements were limited and the illumination optimization methods were lack of universality in current research of illumination optimization method of LED light source for visual inspection system, an illumination optimization method of LED light source for visual inspection system based on improved Salp swarm algorithm, taking visual inspection on chip package quality as example in this paper. A mathematical illumination model of single LED light source was established, based on which the mathematical illumination model of standard strip shape LED array was proposed to obtain the illumination values of the LED array in arbitrary spatial position and measured plane. The plane illumination effect evaluation function was constructed in comprehensive consideration of the illumination uniformity, the average illumination, the illumination gradient variation, the threshold reaching standard, the distinguishability of target and background area. An improved salp swarm algorithm (ISSA) was proposed to optimize the computing procedure of plane illumination effect evaluation function and obtain the spatial position parameters of optimal illumination effect. The update strategies of the convergence coefficients, the Salp speed, the leader and its followers’ position were improved, to enhance the diversity of area searching in ISSA. The experimental results show that based on the observation of the relative illumination distribution of the optimize area, the illumination distribution obtained by the propose method is basically consistent with the illumination distribution by actual measurement, the illumination uniformity of the target area is above 98.78%, and the maximum difference is within 5.57%. Therefore, the proposed method had a reasonable optimization objective and could be used to obtain the spatial position parameters of optimal illumination effect for visual inspection system.