The density operator was induced via V-type atom interacting with a cavity-field through Raman process system in an amplitude damping cavity, and the properties of linear entropies for atom-field system for atom and for field in the system were investigated. The results show that the linear entropy of the system and atom are larger than zero except the initial time in a dissipative cavity. The values remain a certain degree after some time and increase with the increase of mean photon number. At t_d, the atom is completely decoherent to the cavity. The field comes back to the initial pure state. But the atom is still in a mixed state. The larger the dissipation, the more rapid the linear entropies of the atom and system tend to the certain degree of mixture. And the larger the mean photon number, the more obvious the dissipation influence on the linear entropy.