The vibration mechanism of violin bow-string system is very complicated. This paper analyses the traditional stick-slip friction string vibration model and the modern theory of string vibration respectively, as well as the experimental results of string vibration state, then the equivalent pendulum friction vibration model based on energy change is proposed. The model takes into account the changes of energy state of vibration system, and also the vibration period. As a result, the vibration behavior of violin string is reasonably reflected. In this paper, an optical measurement system based on high-speed photography is designed. Through the experiment, the state parameters of string vibration of two different mechanism of plucked and bowed string are investigated. Experimental measurement and theoretical analysis are carried out in particular the vibration displacement and period of points on string, vibration curve’s phase change, transient string vibration state and the envelope of string vibration, hence understands the friction vibration state and characteristics of violin string.