Abstract: This paper presents an expression of pulse compressed Linear Frequency Modulation (LFM) signal with I/Q phase error. The influence of the error on the performance of LFM digital pulse compression is analyzed in detail, a theoretical reference for controlling I/Q phase error in radar receiver designing is provided. The theoretical analysis and the simulating result show that the I/Q phase error will badly influence on the ratio between mainlobe and sidelobe of LFM digital pulse compression with window function for restraining the sidelobe.