Lidar is a powerful tool for atmospheric detection, and its estimation of error is an important content for data processing. In the inversion formula of aerosol backscatter coefficient, it is difficult to calculate the partial derivative of aerosol backscatter coefficient for direct measuring variables, and the conventional error transfer formula can not be applied. To solve the above problem, a direct error formula is proposed, and its reasonability and reliability are tested by comparison calculation. This method can be applied in estimation of aerosol backscatter coefficient total error from molecular extinction coefficient error, aerosol backscatter coefficient error at reference point, lidar ratio error and measuring signal error in lidar data processing.