Abstract: The data of 95 sample trees and 2 165 knots in larch(Larix spp.)plantation were acquired using branch and knot analysis techniques. Using tree and knot factors as independent variables, we developed four models for internal characteristics of knots (ICK), including the knot diameter model, knot angle model, the sound knot length model and loose knot length model. The models described well the changing patterns of factors of ICK, and revealed the mechanism of ICK changes with trees and itself. The results showed that the knot diameter, angle and sound knot length increased with the increase of the height of knot position and DBH. Loose knot length increased with DBH increasing, however the knot itself also had great impact on loose knot length. The results of independent validation showed that prediction precision of each model reached over 95%, thus these models can be applied to forest growth simulation system for increasing the effect of simulation. The studies on variation patterns of ICK also help to reveal the mechanism of branch growth and death, which is of important significance to carry out pruning and therefore improve wood quality.