Exact solutions of (3+1)-dimensional Jimbo-Miwa equation and nonlinear transmission line potential equation are obtained with improved trial function method, including hyperbolic function and trigonometric function solutions. When parameters in hyperbolic function solutions are taken as some special values, the solitary wave solutions can be obtained. When parameters in trigonometric function solutions are taken as some special values, the periodic wave function solutions can be obtained. Practice proves that the trial function method is widely used in the field of nonlinear mathematical physics equations.