The present disclosure relates to an apparatus and a method for improving film thickness uniformity, wherein a PECVD machine with twin chambers comprise a wafer heating platform, which is set to be a rotating platform with programmable speed control, by setting rotating speed of the platform, wafer is rotated for integral rounds within process time, so that a RF overlap between the twin chambers make consistent influence on edge regions of the wafer, and film around the wafer is evenly distributed, which not only eliminate abrupt change of film thickness caused by the RF overlap, but also reduce film thickness differences between edge regions and central regions of the film by a characteristic that the RF overlap improves film deposition rate, so as to ensure the film thickness more evenly in the range of the whole wafer.