The invention discloses an observability analyzing method in power grid harmonic state estimation. The method comprises the steps that 1) mathematical analysis and actual power grid analysis are combined, from the angle of reducing the quantity of state, an equation is changed to be exactly-determined or overdetermined from underdetermined, and the number of measuring devices is greatly reduced on the premise of guaranteeing complete observability of a system state; 2) an SVD method is applied to judgment and calculation of the observable part of a system; 3) the defects of a traditional algebraic method in observability analysis are overcome, the matrix conditional number is combined, a practical linearly independent sorting method is provided and is used for guiding adjustment and addition of the measuring devices of an unobservable system, and the good observability of the system is achieved. Redundancy measuring in the system is found. A measuring mounting point enabling a system measuring-state matrix to be benign is found within the system range. The reservation problem of a decimal point in practical engineering and the problem that a calculation result is unreliable due to the matrix morbidity condition in the calculation process are solved.