The invention provides an interaction correlation-based choleskey decomposition half invariant flow calculating method which comprises the following steps: basic data, node injection power random distribution parameters and response participation factors are input; interaction response node injection power probability distribution and a response correlation coefficient matrix Cres are calculated; Newton-Raphson method flow calculation is conducted at new reference operating points, output variable node voltage X0 and a branch flow Z0 and sensitivity matrixes S0 and T0 are obtained; a choleskey decomposition method is adopted, and node injection power random variables in response correlation are converted into mutually independent random variables; all order half invariants of flow output variables are obtained with response correlation taken into consideration; probability distribution of the output variables is calculated via use of Gram-Charlier series. The method provided in the invention is suitable for analyzing actual operation condition of a power grid after a flexible load used as a high-quality responsive resource participates in system scheduling, and capacity of the power grid in admitting new energy can be further improved.