In this talk, a semi-discrete KP (sdKP) equation is derived from the Hirota-Miwa equation by taking a continuous limit. Bilinear Backlund transformation, Lax pair and a nonlinear superstition formula of the sdKP equation are obtained. Soliton solutions can be given through the nonlinear superstition formula. Then by constructing the Reimann theta functions, we got one-periodic solution and two-periodic solutions, and then analyzed the asymptotic properties of periodic solutions. Finally, we also discussed other kinds of exact solutions such as lump solutions.