The invention discloses a questioning and answering method and device for an open domain of fusing external knowledge. The method comprises the steps that according to a vision problem, discretized external knowledge represented by an explicit expression is extracted from a preset knowledge graph, and the vision problem comprises image information and a problem text; through a knowledge embedded mode maintained by a structure, the discretized external knowledge is embedded in semantic space represented by an implicit expression to obtain a high-dimensional continuous spatial vector; through adynamic memory network and an attention mechanism, auxiliary inference knowledge representation extraction is conducted on the high-dimensional continuous spatial vector, and an image feature is fusedto obtain the answer of the vision problem. According to the method, the superiority of a deep neural network model is kept, a large amount of structural external knowledge is introduced to assist inanswering the vision problem of the 'open domain', the dynamic memory network and the memory mechanism are utilized, the knowledge representation of effectively assisting inference is obtained, and therefore the reliability and effectivity of vision questioning and answering are effectively improved.