In fringe projection profilometry, three-dimensional reconstruction result with higher spatial resolution could provide more detailed description of the measured object. To increase the spatial resolution of three-dimensional reconstruction result, this paper proposes a method to improve the resolution of the absolute phase map recovered in fringe projection profilometry with the digital images of different resolutions. In this method, the same fringe patterns are sampled with the images of different resolutions, the absolute phase maps of different resolutions are obtained respectively. Since the sampling points of the digital images under different resolutions are not coincident, additional ground truth depth information of the object surface is obtained. To emerge an absolute phase map with higher resolution, an algorithm is developed to fuse the absolute maps in different spatial resolutions together. The proposed method can be used to obtain a three-dimensional reconstruction result with higher spatial resolution for various applications. The effectiveness of our proposed method is validated by simulation results.