The double cladding structure can reduce the loss of photonic crystal fiber. A highly nonlinear silica based photonic crystal fiber with double cladding was prepared. Silica based photonic crystal fiber made in our lab was pumped by the femtosecond Ti: sapphire laser in the abnormal region. The effects of the different pump powers and pump wavelengths on mid-infrared ultra short pulse soliton were investigated. Physical mechanisms of the generation of ultra short infrared ultrashort pulses solitons in highly nonlinear silica based photonic crystal fibers were also analysed. In this paper, the first mid-infrared soliton moves from 1933 nm to 2403 nm and the adjustable range lasts for up to 470 nm when the pump wavelength works at 827 nm with the pump power increasing from 0.1 W to 0.42 W. This provides a good condition for the broadband tunable ultrashort pulse source in the silica based photonic crystal fiber.