LEO satellite networks have risen to the forefront of study with the dynamic topology changes, varying service requirements and intermittent inter-satellite links (ISLs). Resource scheduling mechanism is the key to determining communication efficiency. However, the state-of-the-art cannot achieve high resource efficiency under both heavy and burst traffic loads, and the applicability of parameters design is insufficient under intermittent ISLs. Considering this, we propose a dynamic even distribution mechanism combined with network coding DENC. This novel mechanism obtains the service requirements and allocates resources dynamically through the even distribution algorithm to balance between network maintenance overhead and idle resources waste, and improves the success probability of transmission based on network coding to balance between retransmission and redundancy. In this paper, we establish performance analysis and resource efficiency optimization models to optimize the parameters such as maintenance frequency and coding coefficient. Besides, we construct a system-level simulation platform. Mathematical and simulation results indicate that the DENC performs better than SAHN-MAC, ICSMA, CSMA-TDMA and HTM under dynamic service requirements and intermittent ISLs, and the resource efficiency can be improved by about 130%.