The portable micro-X-ray fluorescence analysis with polycapillary optics has advantages of being non-destructive, and it has been widely used in the analysis of cultural relics. However, due to the irregular or curving surface of archaeological objects and the shortcoming of polycapillary optics in focusing X-rays, the distances between the irradiation spot of samples and exit of polycapillary optics are variables. As a result, the sizes of focused X-ray spot can't keep constant, which reduces the accuracy of measurement and the resolution of elemental mappings of scanning area. In this paper, we propose a new type of portable micro-X-ray fluorescence spectrometer that consists of a new closed loop feedback system and SDD X-ray detector, 30W lower power X-ray tube, polycapillary optics, CCD and so on. In particularly, the closed loop feedback system is composed of Laser Displacement Sensor (LDS), stepper motor, sample stage and computer programs developed by LabVIEW languages. During measuring, the LDS accurately controls the distances between the irradiation spot of samples and exit of polycapillary optics. Based on this closed loop feedback system, our portable micro X-ray fluorescence spectrometer can keep the sizes of focused X-ray spot constant. On the other hand, we provide different alternative sizes of focused X-ray spot by controlling the distances between the exit of polycapillary optics and measured spot of samples in our spectrometer. In order to test the feasibility of this instrument, the concentration of elements and elemental mappings of K, Ca, Zn, Fe and other elements in the irregular colored glaze of a piece of ancient porcelain have been measured by our portable micro X-ray fluorescence spectrometer under enabling and disabling LDS conditions. From the results, it can be concluded that the concentration of elements is very close to the real values and the resolution of elemental mappings is better when LDS is enabled. This indicates that the closed loop feedback system based on LDS can accurately reduce the measurement errors caused by the irregular or curving surface of archaeological objects. Therefore, this portable micro X-ray fluorescence spectrometer developed by our laboratory has potential application prospects in non-destructive analysis of cultural relics.