Abstract: Emittance is one of the most important parameters for electron beams. Based on the emittance and transfer martrix, beam envelope and angular divergence can be precisely calculated. Considering the limitation of traditional emittance measurement methods, we employed the multi-slit method to measure the emittance of the laser wakefield accelerated electron beams. In our simulation, the slit width was set as 20 m, the emittance was 0.05 mmmrad. We have achieved a good consistence with 5% relative error between the measured emittance and the given emittance. We also observed the effect of different parameters on the precisions of measured emittance. It is concluded that the slit width is the most important parameter, the emittance measurement is more accurate with the narrower slit width.