In this paper, a fast PMC (Parallel Model Combination) noise adaptation method is proposed for continuous HMM base speech recognizer. The proposed method is realized as a direct reduction of the number of PMC processing times by introducing the distribution composition with the spatial relation of distributions. The proposed method is compared with the basic PMC algorithm in recognition accuracy and adaptation processing time on telephone speech. The result showed that the proposed method saved around 65% (70.9%, - 62.7%) of PMC computation amount with almost no degradation of recognition performance.