The invention belongs to the vision measurement technology and machine element detection, in particular to a multi-camera combination based method for online measuring an engine cylinder combination face hole group. Aiming to design a scheme for quick measuring an engine cylinder combination face hole group based on multiple vision sensors combination and meet the detection requirements of intelligence, quick speed, high precision and low cost in production lines, the invention adopts the technical scheme that two locating holes at the bottom of an engine are taken as a standard to establish a measurement coordinate system, a measurement camera is matched with a high-precision mechanical guide rail driven by a stepping motor for carrying out mechanical scanning to realize circular hole image acquisition of the engine cylinder combination face hole group, meanwhile, a high-precision grating sensor on a grating ruler is used for synchronously measuring the position of a measurement camera acquisition line and at last the diameter and position measurement results of the engine cylinder combination face hole group relative to the measurement coordinate system are obtained by computer digital image processing and space coordinate conversion. The invention is mainly applied to machine element measurement.