A method for obtaining motion information of video images, comprising: determining at least one first candidate reference block in a first reference frame corresponding to a current block in a current frame according to motion vectors of encoded blocks or decoded blocks related in time or space to the current block; determining at least one second candidate reference block in a second reference frame that is respectively corresponding to the at least one first candidate reference block, wherein the determining at least one second candidate reference block in a second reference frame that is respectively corresponding to the at least one first candidate reference block is performed by obtaining a motion vector of the first candidate reference block to the current block according to a position relation between the first candidate reference block and the current block; and determine the second candidate reference block in the second reference frame corresponding to the first candidate reference block according to the motion vector of the first candidate reference block to the current block, wherein the first candidate reference block and the second candidate reference block are symmetrical in proportion with the current block as the center; characterized by calculating a sum of differences between the first candidate reference block and the second candidate reference block that is corresponding to the first candidate reference block, wherein the sum of differences is one of a sum of absolute differences, SAD, a sum of absolute transformation differences, and a sum of absolute squared differences; and selecting the first candidate reference block and the second candidate reference block which have the minimal sum of difference as a first reference block and a second reference block of the current block, and obtaining motion information of the current block according to motion information determined by the first reference block and the second reference block, wherein the motion information determined by the first reference block and the second reference block is two motion vectors of the first and second reference blocks to the current block, respectively, and the motion information of the current block is motion vectors of the current block, wherein the method further comprises: using the two motion vectors, which are determined according to the first reference block and the second reference block, as the motion vectors of the current block. determining at least one first candidate reference block in a first reference frame corresponding to a current block in a current frame according to motion vectors of encoded blocks or decoded blocks related in time or space to the current block; determining at least one second candidate reference block in a second reference frame that is respectively corresponding to the at least one first candidate reference block, wherein the determining at least one second candidate reference block in a second reference frame that is respectively corresponding to the at least one first candidate reference block is performed by obtaining a motion vector of the first candidate reference block to the current block according to a position relation between the first candidate reference block and the current block; and determine the second candidate reference block in the second reference frame corresponding to the first candidate reference block according to the motion vector of the first candidate reference block to the current block, wherein the first candidate reference block and the second candidate reference block are symmetrical in proportion with the current block as the center; characterized by calculating a sum of differences between the first candidate reference block and the second candidate reference block that is corresponding to the first candidate reference block, wherein the sum of differences is one of a sum of absolute differences, SAD, a sum of absolute transformation differences, and a sum of absolute squared differences; and selecting the first candidate reference block and the second candidate reference block which have the minimal sum of difference as a first reference block and a second reference block of the current block, and obtaining motion information of the current block according to motion information determined by the first reference block and the second reference block, wherein the motion information determined by the first reference block and the second reference block is two motion vectors of the first and second reference blocks to the current block, respectively, and the motion information of the current block is motion vectors of the current block, wherein the method further comprises: using the two motion vectors, which are determined according to the first reference block and the second reference block, as the motion vectors of the current block.