Objective To analyze the differences of dosimetry and positioning error between HyperArc and non-coplanar VMAT in patients with brain metastases,provide references for clinical practice.Methods Forty patients with brain metastases were selected.Among them,20 patients who received HyperArc treatment were the observation group,and 20 patients who received non-coplanar VMAT treatment were the control group.Compared the differences in conformal index(CI),gradient index(GI),homogeneity index(HI)of the two groups,as well as the positioning error in the three directions of X(head to foot),Y(left to right),Z(ab-domen to back),and the three rotation angles of Rx(rotation around the X-axis),Ry(rotation around the Y-axis),and Rz(rotation around the Z-axis).Results CI,GI and HI of the observation group were 0.927(0.890,0.950),3.200(2.510,3.730)and 0.220(0.177,0.280),respectively.CI,GI and HI of the control group were 0.888(0.845,0.928),3.340(2.890,4.220)and 0.218(0.180,0.300),respectively.There was sta-tistically significant difference in CI between the two groups(P<0.05),while there was no statistically sig-nificant difference in GI and HI(P>0.05).The positioning error of X,Y,Z,Rx,Ry,and Rz in the control group were 0.118±0.084,0.133±0.112,0.226±0.142,0.930±0.767,1.330±0.869,and 0.910±0.650,respectively,while in the observation group were 0.149±0.113,0.178±0.120,0.172±0.117,1.340±0.758,1.610±0.743,and 1.420±0.832,respectively.There were statistically significant differences in all directions(P<0.05).Conclusion HyperArc performs better in the conformal degree of the target area,but the positio-ning error of Rx,Ry and Rz rotation angles is slightly inferior to that of non-coplanar VMAT.