Abstract: In this paper, on basis of model experiments, the authors tentatively studied the altering regularity of the statical behavior of rock mass influened by chang the length and spacing of grouted rock bolts in soft rock. Under specific conditions, empirical formulas were tiven to show the relation between the characteristic values (including grenrgth and deformation)of rock and the length and spacing of grouted lsock bolts, and that between the equivalent supporting force and the length and spacing of grouted rock bolts.Thus obtained the proper ength of grouted rock bolts. Finally, a simple stress—strain curve (i.e. the constitutive equation)of bolted rock of this kind was suggested.