The invention belongs to the technical field of solar cell manufacturing, and relates to a step-by-step phosphorus doping method of a high-efficiency and low-cost crystal silicon cell, namely a primary depletion diffusion combined with secondary high-concentration shallow layer diffusion and back etching method. By controlling the flow of oxygen, A low-temperature low-phosphorus source depositionis carry out for that first time on a p-type silicon substrate by nitrogen flow rate and phosphorus oxychloride flow rate, After a long time of high temperature propulsion, the phosphorus in the phosphor-silicate glass is exhausted, and the low surface concentration layer n + is realized. The second time, the phosphor-free glass is deposited on the phosphor-silicate glass, and the high surface concentration layer n + + is pushed to form a very thin high concentration layer, which can be quickly etched off by means of back etching. The method can accurately control the phosphorus doping distribution in different regions independently to ensure that the non-electrode region has low doping concentration and low recombination current so as to ensure higher open-circuit voltage. The electrode region has high doping concentration, which forms good ohmic contact with the metal electrode and ensures that the filling factor is not lost, so as to improve the photoelectric conversion performanceof the battery as a whole.