In this paper, we present a multigrid V -cycle preconditioner for the linear system arising from piecewise linear nonconforming Crouzeix-Raviart discretization of second-order elliptic problems with jump coefficients. The preconditioner uses standard conforming subspaces as coarse spaces. We showed that the convergence rates of the (multiplicative) two-grid and multigrid V -cycle algorithms will deteriorate rapidly because of large jumps in coefficient. However, the preconditioned systems have only a fixed number of small eigenvalues depending on the large jump in coefficient, and the effective condition numbers are independent of the coefficient and bounded logarithmically with respect to the mesh size. As a result, the two-grid or multigrid preconditioned conjugate gradient algorithm converges nearly uniformly. We also comment on some major differences of the convergence theory between the nonconforming case and the standard conforming case. Numerical experiments support the theoretical results.Here,/ is an open polygonal domain and f 2 L 2 . /. We assume that the diffusion coefficientfor m ¤ n. Developing efficient solvers/preconditioners for the CR discretization is not only important for its own sake, but it has several important applications. In particular, it can be used to develop efficient solvers for other discretizations of (1.1). For example, by using the equivalence between CR discretization and mixed methods (cf. [1]), the preconditioners for CR discretization can be applied to solve mixed finite element discretizations for (1.1) (see [2,3] for the multigrid algorithms in the case of smooth coefficients). This relationship is also used in [4] to analyze multigrid algorithms for mixed finite element discretization on adaptively refined meshes. Another important application *Correspondence to: Yunrong Zhu, Physical Sciences 318 P. O. Box 8085, 25 is on the design of efficient multilevel solvers for interior penalty discontinuous Galerkin (IPDG) methods; we refer to [5] for the Poisson problem, and to [6] for (1.1) with jump coefficients.A lot of work has been done to develop multilevel solvers and preconditioners for the piecewise linear CR discretization of (1.1) in the context of smooth (or constant) coefficients. Multigrid algorithms were developed and analyzed in [7][8][9][10][11], and two-level additive Schwarz preconditioners are presented in [12]. Hierarchical and Bramble-Pasciak-Xu (BPX)-type multilevel preconditioners were proposed in [13], and their optimality was shown in [14]. Most of the aforementioned works define the multilevel structure using the natural sequences of nonconforming spaces. Because these nonconforming spaces are non-nested, special intergrid transfer operators (restriction and prolongation) are needed in the analysis and implementation of the algorithms. Recently, the robustness of the BPX preconditioner using the non-nested nonconforming coarse spaces was shown in [15] for the jump coefficient problem (1.1).On the other hand, we observe that the standard piecewise linea...