Improving paint quality is of significant importance for vehicle manufacturing. In this paper, a quality propagation model is presented to analyze and improve quality in automotive paint shops. Specifically, we study the vehicle painting process with multiple inspection stations. After each inspection, vehicles failed to achieve quality requirement will be repaired before moving to the next operation. In such systems, the quality variations may propagate along the painting process. To study it, a three-state quality propagation model has been developed, and analytical formulas to evaluate product quality have been derived. In addition, to improve quality performance, a bottleneck analysis method has been introduced to identify the most critical stage that impedes product quality in the strongest manner so that its improvement will lead to the largest improvement of the whole system. To illustrate the applicability of the method, a case study to improve paint quality at an automotive paint shop is introduced.