The present invention provides an analytical method for precipitated particles during co-precipitation reaction, comprising: running a co-precipitation reaction in a reaction vessel to form a precipitated product; injecting a tracking metal to the reaction vessel for a given time duration; collecting the precipitated product containing the tracking metal from the reaction vessel in increments of time to obtain multiple product samples; filtering each collected product sample to separate precipitated particles from filtrate; performing elemental analysis for the tracking metal in the precipitated particles of each collected product sample, to obtain the residence time distribution of the precipitated particles in the reaction vessel according to the concentration of the tracking metal in the precipitated particles. By the analytical method, the preferred residence time of the precipitated particles in the reaction vessel can be ascertained, so that it is clear when the precipitated particles should be collected from the reaction vessel.