Based on the quasi-classical theory, we calculate the zero energy density of states N(B) in the mixed state for a type 11 superconductor. N(B) is related to the sommerfeld coefficient gamma(B), which gives us useful information for a superconducting gap. The linear portion in gamma(B) relative to B,2 and its slope in a low field reflect the gap anisotropy, so that we can distinguish the nodal gap and the anisotropic full gap, and estimate the magnitude of the gap anisotropy. (c) 2005 Published by Elsevier Ltd.