Аннотация:The two-dimensional lattice melting is analyzed in the mean-field approximation within the model involving the long-wavelength fluctuations of the one-particle distribution function and orientational fluctuations of the two-particle one. The transition form is shown to depend on the orientational fluctuation intensity alpha, disclination core energy E(c) and relative core size t. There is a critical value alpha-c larger of which the system melts via two continuous transitions, the dislocation pair dissociation with the formation of hexatic phase taking place in the first transition and hexatic phase converting into usual liquid via disclination pair dissociation in the second one. In the last transition line the universal relation a0(2)n0(T(i)) = pi/108 holds on, where n0(T(i)) is the free dislocation density. For alpha < alpha-c, the system melts through two continuous transition with the disclination core energy larger the critical one E(c)*. For E(c) < E(c)*, the system melts through one first-order transition when the dissociation of disclination complexes occurs. The first-order transition parameters depend on E(c), t and alpha.