Coordination of hydro power with multiple renewable sources is an effective way for reducing the adverse effects of large-scale renewable energy integration on the power system. The coordination takes advantage of complementary nature among renewables and the dispatchability feature of hydro stations. This paper presents a yearly scheduling model of the hydro-PV-wind hybrid system, maximizing its generation power and constrained by the total firm power limits. Total firm power constraints ensure the reliability of the hybrid system's monthly generation and reduce the influence of generation. However, the probability distributions of wind power, water inflow and solar radiation are difficult to predict and they are the basis of stochastic optimization. Thus, interval optimization is employed to solve this problem by only considering the possible intervals of random variables. Interval optimization not only reduces the errors introduced by distribution assumptions, but also acquires the possible intervals of the objective value and state variables. To handle the constraints containing intervals, a pessimistic preference ordering of interval numbers is also employed. This interval optimal scheduling model is illustrated and compared for a realistic case study in Yunnan.