The invention discloses a multi-index extensible evaluation method for dangerous rock falling ricks in tunnel and underground engineering. The method comprises the following steps of: 1, establishing a dangerous rock falling risk evaluation index system according to main factors inducing side slope dangerous rock mass collapse; 2, establishing a grading standard for dangerous rock falling risk evaluation and determining a dangerous rock falling risk evaluation grade; 3, quantifying or correcting an evaluation index parameter, namely, normalizing and scalarizing a qualitative index, and describing the qualitative index to a certain extent by using a numerical value form; 4, establishing a classical domain, a joint domain, a to-be-evaluated matter element and an extensible model of a to-be-evaluated dangerous rock matter element; 5, collecting to-be-evaluated dangerous rock data, determining a weight of each risk evaluation index by adoption of a single correlation function method, and calculating a correlation function value of the to-be-evaluated dangerous rock matter element; and 6, evaluating the dangerous rock falling risk, and calculating a grade variable feature value of the to-be-evaluated matter element so as to obtain a collapse rock falling risk grade of a to-be-evaluated dangerous rock at a portal section of a tunnel.