Newton's second law and the law of gravity are summarized with experimental results. For discussing the possibility of deriving the two laws theoretically, according to the law of conservation of energy, the method of deriving improved Newton's second law and the law of gravity at one time with variable dimension fractal method is presented for an example (a small ball moves down along a long incline). For the sake of convenience, the results suitable for this example with the constant dimension fractal form are as follows： improved law of gravity F = - GMm/r^1.99989 , and improved Newton's second law F = ma^1.01458.