The invention discloses a method for predicting congestion duration and spatial 
diffusion of 
urban road traffic. The method comprises the following steps of: (1) carrying out 
cell division on an area constituted by a target road section, an upstream road section and a downstream road section according to a 
road traffic flow characteristics after initial congestion occurs, wherein 
tail cells are defined as the cells located at a canalization region at downstream outlets of the road sections; (2) initializing each key parameter of each 
cell; (3) making a judgment according to a judgment rule (1) of the 
cell of the target road section after each 
time step is up, and with respect to the cells of the upstream road section and the downstream road section, making judgments according to a rule (2) and a rule (3) respectively in an 
observation period after each 
time step is judged to be up; and (4) if a termination condition of the judgment rule (1) is satisfied, terminating the judgment and calculating to predict the congestion duration, or else, turning to (3), and if the termination condition of the rule (2) or rule (3) is satisfied, terminating the judgment and calculating to predict congestion 
diffusion time, or else, turning to (3). The method disclosed by the invention can be used for effectively predicting the congestion duration and carrying out spatial 
diffusion estimation and is good in practicability.