Abstract: Wellbore anti-collision is an important difficulty in the construction of directional wells of dense cluster wells. In order to effectively reduce the collision risks of the vertical sections of the infill wells of dense cluster wells, a new comprehensive method for calculating the wellbore collision risks of dense cluster wells was put forward by considering nominal spacing, diameter sum of reference well and comparison well and number of neighboring wells comprehensively after the probability based Brooks wellbore collision evaluation method was analyzed. In this new method, a circle is set by taking the central axis of the wellbore of reference well as the center and the nominal spacing between reference well and comparison well as the radius. Migration probability is calculated by using the ratio of the diameter sum of reference well and comparison well to the circumference of the circle, and the collision probability is calculated by using the definite integral of the probability density function of normal distribution at the coordinate of wellbore measurement point in the direction of well depth. The actual collision probability between reference well and comparison well is the product of the migration probability and the collision probability. The comprehensive collision probability is determined by summing the collision probability between the reference well and each comparison well, and it is classified into three risk levels according to industry standards. In this way, a collision risk evaluation method that takes the comprehensive collision risk as an evaluation index is developed. This method can quantitatively evaluate the comprehensive collision risk between a reference well and multiple comparison wells, and is of important significance to anti-collision theory research and production practice guidance of infill wells.