Aiming at the undesirable wireless-side communication condition in MEC systems, a multiaccess MEC system model assisted by UAV mounted RIS was proposed. It fully utilizes the computational resources of each network nodes for parallel processing and dynamically deploys the RIS via mobility of UAV to enhance channel conditions. The optimization problem of the above-mentioned model requires simultaneous adjustments to users offloading schemes, UAV deployment position, and RIS phase shift matrix to maximize energy efficiency while satisfying system latency constraints. Due to the high-dimensional and non-convex nature of this optimization problem, which prevents gradient-based optimization or direct mathematical solution, an improved DE algorithm based on individual similarity ISDE is introduced. ISDE divides the population into exploration and exploitation subpopulations to strengthen global exploration and local exploitation capabilities. Experimental results demonstrate that the proposed system and optimization method achieve higher energy efficiency compared to traditional MEC systems and existing algorithms.