A cyclone over the Arabian Sea has lots of effect on people's life in India and it sometimes bring Indian summer monsoon. In the present study, cyclogenesis and its development over the Arabian Sea are investigated by using satellite observation data and atmospheric reanalysis data. There is large temperature gradient around the coastal area of the Arabian Peninsula between warmer air over land and cooler air over ocean. Baroclinic instability by the horizontal temperature gradient in that region easily generates a seed of cyclone at 850hPa. Regarding development of cyclone over the Arabian Sea, water vapor over the region of a seed of cyclone does not show significant difference between development and non-development case. On the other hand, occurrence of air disturbance in middle-upper troposphere and coupling of upper and lower air disturbances are considered to be more important for the development of cyclone over the Arabian Sea.