Abstract: Self-adaptive systems are able to adjust their behaviour in response to environmental condition changes and are widely deployed as Internetwares. Considered as a promising way to handle the ever-growing complexity of software systems, they have seen an increasing level of interest and are covering a variety of applications, e.g., autonomous car systems and adaptive network systems. Many approaches for the construction of self-adaptive systems have been developed, and probabilistic models, such as Markov decision processes (MDPs), are one of the favoured. However, the majority of them do not deal with the problems of the underlying MDP being obsolete under new environments or unsatisfactory to the given properties. This results in the generated policies from such MDP failing to guide the self-adaptive system to run correctly and meet goals. In this article, we propose a systematic approach to updating an obsolete MDP by exploring new states and transitions and removing obsolete ones, and repairing an unsatisfactory MDP by adjusting its structure in a more meaningful way rather than arbitrarily changing the transition probabilities to values not in line with reality. Experimental results show that the MDPs updated and repaired by our approach are more competent in guiding the self-adaptive systems' correct running compared with the original ones.