The discovery of XYZ particles is a big challenge for quark model. The model must be extended. By considering the high Fock components, an unquenched quark model is developed. The improved quark-pair creation operator in 3P0 model is invoked to deal with the mixing between quark-antiquark and meson-meson states. Gaussian expansion method is employed to do a high precision calculation of this few-body problem. Applying the unquenched quark model to light meson systems, a reasonable results are obtained. Applying to charmonium states, X(3872) can be reproduced as a mixing states of ccbar (70%) and DD* states.