P(r ,t ,x) denotes the population density of age r at time t and in spatial position x ,B denotes the fertility rate of females of age r at time t and in spatial position x, U denotes the mortality rate of age r at time t and in spatial position x, Q denotes the Laplace operator with respect to the space variable ,K>0 is the diffusion coefficient.
F Denotes effects of external environment for population system, such as emigration and earthquake and so on. The effects of external environment has the deterministic and random parts which depend on r ,t and x .W is a standard Wiener process.