Luodian, located in the southern Guizhou Province, belongs to the outer zone of Emeishan Large Igneous Province. Numerous diabase of the same period as the Emeishan Large Igneous Province are exposed in the area. The acidic dykes are quartz monzonite porphyry, and invade into diabase. The study of acidic dykes is conducive to enriching the understanding of the law of lithology combination and magmatism in Emeishan Large Igneous Province. Petrology, SIMS chronological and geochemical studies of the acidic rock in Luodian were performed. Average content of major oxides are SiO₂ 66.83%, Cao 1.76%, Al₂O₃ 14.74%, MgO 0.76%, TFe₂O₃ 4.49%, K₂O 3.67%, Na₂O 5.24%, and average value of A/CNK is 0.93, displaying the features of high silicon, rich alkali and quasi-aluminous. (La/Yb)_N ratios of 7.71 to 10.60 displays apparent differentiation between LREE and HREE with an average δEu of 0.91. The chondrite-normalized curve of REE is right inclined, showing ocean island basalts (OIB) signature. The dykes are enriched in elements such as Rb, Ba, Th, K and Nd, and depleted in elements such as Nb, Ta, P and Ti. The values of (⁸⁷Sr/⁸⁶Sr)_i (0.704247-0.705292) and ε_Nd(t)(1.08-1.54) are similar to those of diabase. It is suggested that the acidic rock is originated from fractional crystallization of basaltic magma produced by partial melting of mantle plume, and contaminated with a small amount of upper crust material. The acidic rock was dated at (259±2) Ma by SIMS, which is consistent with the magmatism age of the Emeishan Large Igneous Province. The large number of inherited zircons in the samples were found, might be the response to tectonic activity at different stages in the Yangtze block.