The Haidewula uranium deposit is the first typical volcanic-related hydrothermal uranium deposit to be discovered in northwest China currently. Revealing the nature of the ore-forming fluids and the mineralized mechanism is favorable to understand the genesis of the deposit and to guide the prospecting in this area. Detailed studies on mineralogy, petrography and trace elements of fluorites from the deposit have been conducted in this paper. The results show that two stages of hydrothermal fluorite including metallogenic stage dark purple fluorite and post metallogenic stage purple fluorite have been identified, with the metallogenic stage dark purple fluorite closely associated with the uranium mineralization. The characteristics of trace elements and the REEs pattern are significantly different in two stage fluorites. The dark purple fluorite in the metallogenic stage is relatively enriched in Sr and Ba, while the purple fluorite in the post metallogenic stage is relatively enriched in REE and trace elements such as Co, Ni, Cu, Zn, Ga, Rb, Y, Zr, Nb, Mo, Cs, Pb, Th and U. The ΣREE of dark purple fluorite in the metallogenic stage ranges from 59.98×10-6 to 118.31×10-6, with a median value of 75.02×10-6, and the REE pattern is characterized by enriched LREE (LREE/HREE ratios median 5.06) and a strong fractionation between LREE and HREE ((La/Yb) N value median 12.24)), with moderate negative Eu anomaly (with median of 0.56), week Ce anomaly (with median of 0.99) and positive Y anomaly (with median of 2.21). The ΣREE of purple fluorite in the post metallogenic stage ranges from 194.12×10-6 to 207.67×10-6, with a median value of 195.55×10-6. The REE patterns of purple ?uorite is characterized by enriched LREE (LREE/HREE ratios median 4.76) and a relatively strong fractionation between LREE and HREE ((La/Yb) N value median 6.37)), with a well-pronounced negative Eu anomaly (with median of 0.09), positive Ce anomaly (with median of 1.33) and positive Y anomaly (with median of 1.90). Based on the comparison with the geochemical characteristics of the surrounding rocks and the pitchblende, two stages of fluorite (metallogenic stage dark purple fluorite and post metallogenic stage purple fluorite) in Haidewula uranium deposit were formed in the fluids with different sources. The metallogenic stage dark purple fluorite was formed in the acidic ore-forming ?uid rich in F- and Cl-, and maybe precipitated by the mixing mechanism of meteoric water with magmatic water in a reducing environment. The trace element geochemical characteristics of post metallogenic stage purple fluorite, such as with Ce positive anomaly and inheriting the Eu negative anomaly of the ore-bearing volcanic host rocks, indicated that the fluorite was formed in the oxidizing environment with higher proportion of meteoric water and higher oxygen fugacity and pH value in the fluid.