Abstract: In this paper,pulp ＆ paper sludge biochar is used as a carrier to prepare a solid base catalyst and applied to the preparation of biodiesel. The physicochemical properties of the catalyst were analyzed by thermogravimetric analysis（TGA）,scanning electron microscope ＆ energy dispersive spectrometer（SEM-EDS）,Fourier transform infrared spectroscopy（FTIR）,X-ray diffraction（XRD）,N2adsorption/desorption and CO2-TPD for characterization. The results show that 30K/PPSB-600 has the highest total alkalinity,and it has excellent catalytic activity（maximum biodiesel yield is 98.5%）. In addition,the stability and reusability of the catalyst were also examined. After 8 times of repeated use,the catalyst still has high catalytic activity（biodiesel yield is 80%）. The small amount of catalyst deactivation is mainly due to the loss of K+ions.