The technique of laser sheet beam has been applied to optically accessible diesel engine for the quantitative measurement of soot. The results provide the information for us for reduction of soot in diesel engine. We used both LIS nad LII techniques simultaneously in this study. LIS and LII images show the quantitative distribution of the soot concentration in an optically accessible diesel engine. In this study, several results were obtained by the simultaneous measurement of LIS and LII technique. The diameter and number density of soot in combustion chamber of the test engine were obtained from ATDC 20$^{circ}$ to 110$^{circ}$ . The increase rate of soot diameter was about 40$^{circ}$ between ATDC 20$^{circ}$and 110$^{circ}$. And the number density of soot decreased significantly between ATDC 20$^{circ}$and 40$^{circ}$.