Relation of definite integral and indefinite integral was discussed and an important result was gotten. If f（x） is bounded and has primary function, the formal definite integral \int^x_s \tilde{f}（t）dt is the indefinite integral of f（x）, where x is a self-variable, s is a parameter,\tilde{f}（x） is a function defined in（-∞, +∞）, which comes from f（x） by restriction and extension. In other words, the indefinite integral is a special form of definite integral, its lower integral limit and upper integral limit are all indefinite. 

Relation of definite integral and indefinite integral was discussed and an important result was gotten. If f（x） is bounded and has primary function, the formal definite integral \int^x_s \tilde{f}（t）dt is the indefinite integral of f（x）, where x is a self-variable, s is a parameter,\tilde{f}（x） is a function defined in（-∞, +∞）, which comes from f（x） by restriction and extension. In other words, the indefinite integral is a special form of definite integral, its lower integral limit and upper integral limit are all indefinite.