TMS320F28234: MCU abnormal when a large current occurs

By “large current”, I presume you are referring to the current in your power-stage and not current consumed by the device itself. The fact that the RAM contents get corrupted and the Watchdog initiates a reset (presumably due to the program Counter getting corrupted) suggests that the device is getting impacted by EMI.

ESD/EMI events are capable of inducing all sorts of bizarre behavior in the device, including “locking up” or “freezing” the device. While a watchdog reset (or an external “warm” reset, by way of activating the -XRS pin) generally pulls the device out of this indeterminate state, sometimes cycling power is the only way to get the device to function normally again. The solution lies in hardening the circuit design to make it immune to the disturbance. The challenge lies in determining precisely how the disturbance impacts the circuit. i.e. in identifying exactly how noise couples into the circuit. In other words, what is the conduit for this noise to get into the circuit and cause the malfunction? Once this is identified, it is relatively easy to come up with the protection solution. Unfortunately, often times, the shortcomings are discovered after the board is made and hence make the redesign of the board necessary. 

Many books have been written on this topic and many papers published. The actual circuit design, the components used, the geometry of the components, the board layout, the board stack-up, the shielding employed , all play a role in the immunity strength of the design. Debugging such problems is an iterative process and warrant hands-on debug. It is extremely difficult to debug issues like this remotely, without access to the schematics, PCB layout and the hardware itself. In other words, remote debug is not practical. The first task is to find whether the noise is coupled conductively or radiatively into the system. i.e. whether the issue at hand is one of conducted immunity or radiated immunity. Once this is identified, we need to identify the entry point of the noise into the system. Only then can we come with a solution. Problem could be related to insufficient decoupling/filtering, incorrect layout, improper (or lack of) shielding etc. There are numerous resources online that deal with this. Hard to explain them in a post. Please google "EMC shielding" for helpful links.

Li Jian Xian said:

I want to ask how this large current affects the MCU?

Large current translates to larger switching noise and  a stronger electromagnetic field.

Li Jian Xian said:

Does it may affect the MCU through conduction?(through digital IO? power pin? ground?) or through radiation?

Any of the above could serve as a conduit.

Li Jian Xian said:

Does this MCU has some EMC specifications on the document?

No.