Though microlens arrays have been used to enhance luminance efficiency and luminance power efficiency of light-emitting diodes (LEDs) and organic LEDs, the influence of the parameters of a microlens array on the efficiency improvement has not been systematically discussed. In this study, the influences of the edge length and the gap of the microlens array on the luminance efficiency, CIE index and optical emitting spectrum of planar OLED devices will be explored. Additionally, a method of analyzing the performance of the luminance efficiency improvement of the device per single microlens in a microlens array of known microlens number density is to be demonstrated.