A measuring method for intra-cavity loss of an all-solid-state laser includes the steps: firstly, measuring output power of the all-solid-state laser with a power meter; then, measuring intensity noise of the all-solid-state laser under the output power by an automatic zero-beat detecting system, and determining a relaxation oscillation frequency value of the all-solid-state laser; and finally, computing with an intra-cavity loss expression including the output power and the relaxation oscillation frequency value of the laser, so that an intra-cavity loss value of the laser can be obtained. The measuring method is suitable for measuring intra-cavity loss of the all-solid-state laser of a non-injection locking structure.