A simple density gradient measurement system for 2D flow fields was proposed.The system introduced a grating into the traditional schlieren system and transformed deflection rays caused by density change of a flow field into the deformation of fringe pattern formed by grating projection,so density gradient information of the flow field could be extracted from the deformed fringe pattern.With wavelet location characteristics,a wavelet transform phase demodulation method was applied to fringe pattern analysis to eliminate effect of invalid data effectively.Experimental results indicate that the measuring range of the system can reach 0.01 g/cm⁴ and the measurement precision can reach 5×10^-6 g/cm⁴,which shows proposed system is simple in setup,easy in adjustment and suitable for density gradient measurement for flow fields with large density variation.