The invention relates to the technical field of sensor preparation, particularly to a flexible force sensor and a preparation method thereof, an array device, and application of a flexible force sensor. A microstructured film is made by PDMS, so that the structural elasticity is enhanced by the low Young's modulus of PDMS and the wearability and sensitivity of the flexible force sensor are strengthened; on the basis of a surface-bionic random multilayer microstructure, the sensitivity of the sensitive sensor is enhanced substantially and the sensing capability to the micro stress is improved;and thus the piezoresistive flexible force sensor can be applied to health fields such as medical monitoring so as to monitor various body signals like the pulse and breathing in real time. Besides, the preparation method of the flexible force sensor has the high processability and low cost, so that large-scale production is realized well. And with the method provided by the invention, bionic surfaces with different shapes, different levels, different scales, different dimensions, and different functions can be obtained.