The Helmholtz scattering problem with high wave number is truncated by the perfectly matched layer (PML) technique and then discretized by the linear continuous interior penalty finite element method (CIP-FEM). It is proved that the truncated PML problem satisfies the inf-sup condition with inf-sup constant of order O(k −1 ). Stability and convergence of the truncated PML problem are discussed. In particular, the convergence rate is twice of the previous result. The preasymptotic error estimates in the energy norm of the linear CIP-FEM as well as FEM are proved to be C1kh + C2k 3 h 2 under the mesh condition that k 3 h 2 is sufficiently small. Numerical tests are provided to illustrate the preasymptotic error estimates and show that the penalty parameter in the CIP-FEM may be tuned to reduce greatly the pollution error. R 0 J n (kt)f n (t)tdt.(2.24)Note that from [49, 10.21(i)], the zeros of J ν (z) are all real for ν ≥ −1. SinceR is not real and J −n = (−1) n J n for integer n, we have J n (kR) = 0, n ∈ Z.