A kind of fusion dianostics based on proton recoil method and magnetic analyzing technology is introduced. It can be used for the accurate diagnoses of plama tempreture, fuel density and neutron yield. A prototype is designed, using a high-powered Nd-Fe-B permanent dipole for magnetic analyzer, and proton position distribution in the focal plane is measured by CR-39 trajectory detector or PIN detector. The system is calibrated with a 239 Pu source, and a corresponding particle transport simulation program is worked out. The performance of the spectrometer is investigated with the Monte Carlo simulation, and neutron experiments are taken on the K-400 accelerator.