The measuring sensor will produce incidence Angle difference when we use new laser measuring diameter instrument to measure the diameter of filter rod due to the irregularity of filter rod forming. How to eliminate the measurement error of laser caliper gauge and get the measured value closest to the real value of diameter is the key question. The optimal diameter estimation method was used to obtain the optimal combination of measuring angles. Then the average values of different angle combinations were calculated as the estimated values, to reduce the measurement error caused by the difference of incidence angle. Using the optimal diameter estimation method, the average value of the four values with an interval of 45 ° in range of 15 °~165 ° of the filter rod was selected as the measurement estimated value of filter rod. The difference of this value and the true value of filter rod diameter met the requirements of measurement precision (±0.01 mm). This method effectively reduced the error introduced by the different incidence angle, and gave the optimal measuring angle distribution value. In conclusion, optimal diameter estimation method could provide guidance in reasonable selection of the measuring angle distribution and effectively reduce the measurement error caused by the difference of Incidence Angle.