Vertical wind shear is one of the most important factors contributing to the spatial distribution of Tropical cyclone (TC) rainfall. This study adopts wavenumber-1 Fourier Coefficients to compute the TC rainfall asymmetry caused by environmental shear based on TRMM TMPA rainfall estimates of 439 TCs from 1998 to 2012 over Northern West Pacific basin (NWPAC). The environmental vertical wind shear is defined as the difference of wind vectors between 200- and 850-hPa levels over a region of 200-800km from TC center. It is calculated based on the NCEP reanalysis wind dataset. TCs are divided into groups according to the TC intensity (CMA CAT2, CAT34, CAT56) and environmental shear strength (7.5-10, 10-15 and >15m/s), respectively. The shear-relative asymmetric TC rainfall shows a general left-to-right asymmetry. The positive wavenumber-1 asymmetry rainfall is down-shear left or down-shear for three TC intensity groups, and the maximum asymmetry is down-shear left in the inner 150-km. The magnitude of asymmetry rainfall decreases slightly with the increase of TC intensity. In terms of shear, the positive wavenumber-1 asymmetry is down-shear left especially when shear value >7.5m/s. The amplitude asymmetry increases with the increasing strength of environmental shear.