An approximate method is proposed for the measurement of intensity-energy [I(E)] curves of low-energy electron diffraction at the normal incident condition. In this method only two equivalent spots located in the horizontal direction are optimized to have identical I(E) curves. It is found that I(E) curves obtained by this method approximate well those at the exactly normal incident condition, as long as the total misalignment is less than 1-degrees. The reason for the success of this method is discussed. Advantages and disadvantages of this method are presented. It is emphasized that reproducible I(E) curves can be obtained easily due to a clear guideline of this method.