Abstract: The decomposition of medium-and long-term contract is one of the key links in the electricity market. A fair and reasonable decomposition algorithm can not only effectively connect the spot market and medium-and long-term contracts, but also provide the guarantee for the safe and stable economic operation of the power system. As the generation units such as nuclear,hydropower, gas with different output characteristics participate in market transactions jointly, the contract decomposition method is faced with many practical problems that need to be studied urgently such as output characteristics of differentiated units,maintenance scheduling and market power risk reduction. In this paper, a joint decomposition algorithm of contracts for different types of units considering market power test is proposed. First, by analyzing the operation characteristics of different types of units,the decomposition principles for nuclear, hydropower, gas and coal units are designed. Then, based on the principle of the priority of operation modes, a joint decomposition model of contract considering the maintenance scheduling of sets and output characteristics of various units on the generation side is established. Finally, in order to avoid the abuse of the market power of units, the rationality of the contract decomposition result is checked with the index of"must-run generation（MRG）". A case of modified IEEE 24-bus system with load characteristics of a province in east China shows that the proposed algorithm has advantages in adaption to operation characteristics of various units and suppression of market power.