Quantum gas microscopy has enabled the study on intriguing properties of ultracold atoms in optical lattices.It provides the cutting-edge technology for manipulating quantum many-body systems.In such experiments,atoms have to be prepared into a two-dimensional (2D) system for being resolved by microscopes with limited depth of focus.Here we report an experiment on slicing a single layer of the atoms trapped in a few layers of pancake-shaped optical traps to create a 2D system.This technique is implemented with a microwave "knife",i.e.,a microwave field with a frequency defined by the resonant condition with the Zeeman-shifted atomic levels related to a gradient magnetic field.It is crucial to keep a stable preparation of the desired layer to create the 2D quantum gas for future experimental applications.To achieve this,the most important point is to provide a gradient magnetic field with low noises and slow drift in combination with a properly optimized microwave pulse.Monitoring the electric current source and the environmental magnetic field,we applied an actively stabilizing circuit and realized a field drift of 0.042(3) mG/hour.This guarantees creating the single layer of atoms with an efficiency of 99.92(3)％ while atoms are hardly seen in other layers within 48 hours,satisfying future experimental demands on studying quantum many-body physics.