Abstract: The major factor of restricting grain crop production is soil moisture on the Songnen Plain (Heilongjiang Province), and it is extremely necessary to discuss sequential variation of it for to know developing process during the climate variety of the world. Based on soil moisture during crop growth of every ten-day from 1980 to 2010 of 16 agro-meteorological stations, it had analyzed characteristic of soil moisture space time variation on the 0-30 cm layer in crop growth season by Mann-Kendall method. The results showed that, the variation of topsoil moisture near 30 years coincides with each other in different regions of Songnen Plain, which trend is decreasing. In the 1980s, topsoil of most area had been moist, and individual counties’soil was arid in several years. In the 1990s, the soil moisture had been descending obviously, and it developed from moist to arid step by step, and it had high frequency arid years, that is to say, there is aridity trend. The soil moist of the south area was not decline trending obviously from M-K breakpoint tests. The breakpoint of the north was in 1991, and the east was in 2002, the west was in 1997, and the middle area was in 1991.