A system based on personal digital assistant（PDA）for automatical counting blood cells is introduced.This system has the advantages of easy operation

small volume

high accuracy

etc

which overcomes the shortages of complex structure and big volume.It satisfies the demand of counting check outdoors.Microscope

CCD camera and PDA compose the system.Using eVC++4.0 the programs are written in WIN CE OS（operating system）for real time observation

processing of the cell image and acquiring the cell numbers directly.The system uses many methods of image processing including two dimensions maximum entropy for image segmentation

region growing

role filling

region labeling

etc and realizes automatical counting of red cells

white cells and blood platelets.The results show that the relative error automatical counting compared with manual counting is lower than 5 %.