The invention discloses a preparation culturing method capable of avoiding pollution effectively for conidia of magnaporthe oryzae. High-quality conidia of the magnaporthe oryzae are prepared and cultured by taking a common conical flask as an appliance for preparing and culturing the conidia. The preparation culturing method comprises the following steps: (1) cleaning the common conical flask for later use; (2) taking a flask type oat culture medium; (3) planting mycelia of the magnaporthe oryzae into the flask type culture medium; (4) performing conidium producing culture at the temperature of 28 DEG C; (5) eluting and collecting the conidia. The preparation culturing method has the advantages that: (1) pollution can be prevented efficiently, and the quality of finished conidia is high; (2) the operation technology is simple; (3) the operation of collecting the conidia from the conical flask is more convenient than the operation of collecting the conidia from a culture vessel, conidium producing colonies can be placed for a period of time randomly without being polluted under the protection of the conical flask, and the conidium producing state can be maintained so as to link with a working process which requires the conidia conveniently.