This paper deals with the spatial variation regularities of cosmic radiation and the estimation of exposure doses to aircews. The instruments used for measurement were RSS-111 high pressure ionizing chamber, FD-3013 scintillation radiometer and BF3 proportional counter. Measurements were made in 15 types of aircraft on 55 flights, and also made in 5 types of aircraft at different altitudes over 10 airports. The measurements covered altitudes ranging from 0.5 to 15 km and geomagnetic latitudes ranging from 7° to 65°N. By measurements, the spatial variation regularities of cosmic radiation were deduced and the empirical formulas for ionizing component were obtained. The lowest value of annual effective dose received by a crew member who worked as many as 1000 hours a year would be 0.27mSv, the median value 4.19mSv and the highest value 10.56mSv. Even the highest dose is considerably lower than the annual occupational limit of 20 mSv （averaged over five years） recently recommended by the International Commission on Radiological Protection. Some results of this study are compared with those in relevant published literature.