The invention provides a method and an apparatus for determining the development degree of rock cracks. The development degree of all micro-crack groups in an axial extension direction and in a transverse expansion direction is quantified. The method comprises the following steps: constructing a grain flow model of a rock sample; acquiring a micro-crack set in the destroy process of the grain flow model and the coordinate value of every micro-crack point in the micro-crack set according to the constructed grain flow model; carrying out clustering based on the density of the micro-crack points according to the obtained micro-crack set and the coordinate value of every micro-crack point in the micro-crack set, and grouping the micro-crack points in the micro-crack set according to the distance of every clustering center to obtain multiple micro-crack groups; and analyzing the axial extension direction and the transverse expansion direction of every micro-crack group by adopting a main component analysis technology, and quantifying the development degree of every micro-crack group in the axial extension direction and in the transverse expansion direction. The method and the apparatus are suitable for the technical fields of rock soil test and engineering.