The　theoretical　research　on　raindrops　movement　should　promote　water　conservation　in　the　Loess　Plateau.　Four　influence　factors　on　the　raindrops　falling　in　the　Earth　atmosphere　were　studied,　which　include　gravitational　force,　buoyancy,　viscous　resistance　and　Coriolis　force.　Three　mathematical　models　on　raindrops　were　established　with　Newton＇s　dynamic　equation.　Simulated　to　the　equations,　all　characteristics　of　raindrops　falling　were　obtained.　The　research　shows　that　the　raindrops　have　different　terminal　falling　speed　as　different　size　due　to　the　viscous　resistance.　The　buoyancy　is　almost　no　influence　to　all　characteristics　of　raindrop　falling.　The　Coriolis　force　leads　raindrops　to　move　eastward　and　southward,　as　well　as,　the　eastward　migration　is　more　obvious　than　the　southward.　The　raindrops　falling　migration　from　the　viscous　resistance　action　is　very　significant.