Miniaturization of chromatography is an important tendency in development of modem analytical instrument.Microfluidic chip is a powerful platform to achieve the goal of miniaturization of chromatographic apparatus by integrating all the function units on a single chip.However, the fabrication of high-pressure valve for small-volume injection in microchip-based high-performance liquid chromatography (HPLC) device is a challenge.Yin et al.[1] developed an integrated microfluidic device integrating an injection valve, an enrichment column, and a reversed-phase separation channel on a polyimide chip.However, the integration of valve in microchip requires high-precise microfabrication technique and expensive equipments, which is difficult to realize in routine laboratories.Here, we report a simple approach for sample injection in microchip-based HPLC system with a monolithic LC column.