Because the detecting of the small target in the background of sea clutter is strongly dependent on sea condition, in this article we use fractional Brownian motion to model IPIX sea clutter and combine multifractal detrended fluctuation analysis (MF-DFA) to determine the fractal parameters for analyzing fractal and multifractal property of IPIX sea clutter. Based on the fact that Hurst parameter and fractal dimension can reflect the fractal property of data, a new parameter named fractal differential which has difference when the sea clutter with or without target is defined, thereby solving the problem of small target in sea clutter background. By comparing the multifractal parameters of two sea clutter, the experimental results show that H(q) is a special value which is bigger than zero when the sea clutter has a small target but smaller than zero when the sea clutter has no target if q is bigger than ten. Another method is proposed by using the difference of H(q). Two methods in this article can solve the problem of strong dependence of detecting the small target in different sea conditions on sea condition.