To investigate the influence of center distance error on tooth strength of small modulus gear and the applicability of GB/T 3480—2021 to the strength design of small modulus gear with center distance error， the calculation formulas of the contact coefficient， tooth profile coefficient， and stress correction coefficient are deduced by introducing center distance error. Then， the finite element model of small modulus gear with center distance error is established， and the verifying method to determine the mesh density is proposed. The contact stress and bending stress under different center distance errors obtained by the two methods are compared， and the results show that when the width of the element in the tooth profile contact area does not exceed 1/3 of the Hertz contact half-width， this contact model has a good calculation accuracy. The use of GB/T 3480—2021 to check the strength of small modulus gear with center distance error will produce a redundant design； when the center distance error reaches 1.33%， the maximum change of the contact stress amplitude is 4.23%， and the maximum change of the bending stress amplitude is more than 16.25%. The influence of center distance error on the bending stress of small modulus gear is more significant than the contact stress.